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Introduction: coronavirus disease 2019 (COVID-19) transmission dynamics in the communities of low- and middle-income countries, particularly sub-Saharan African countries, are still not fully understood. This study aimed to determine the characteristics of COVID-19 secondary transmission during the first wave of the epidemic (March-October 2020) in Lusaka, Zambia. Methods: we conducted an observational study on COVID-19 secondary transmission among residents in Lusaka City, between March 18 and October 30, 2020. We compared the secondary attack rate (SAR) among different environmental settings of contacts and characteristics of primary cases (e.g, demographics, medical conditions) by logistic regression analysis. Results: out of 1862 confirmed cases of COVID-19, 272 primary cases generated 422 secondary cases through 216 secondary transmission events. More contacts and secondary transmissions were reported in planned residential areas than in unplanned residential areas. Households were the most common environmental settings of secondary transmission, representing 76.4% (165/216) of secondary transmission events. The SAR in households was higher than the overall events. None of the environmental settings or host factors of primary cases showed a statistically significant relationship with SAR. Conclusion: of the settings considered, households had the highest incidence of secondary transmission during the first wave in Lusaka, Zambia. The smaller proportion of contacts and secondary transmission in unplanned residential areas might have been due to underreporting of cases, given that those areas are reported to be vulnerable to infectious disease outbreaks. Continuous efforts are warranted to establish measures to suppress COVID-19 transmission in those high-risk environments.

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The implementation of isolation precautions for patients with suspected Coronavirus Disease 2019 (COVID-19) and pending test results is resource intensive. Due to the limited availability of single-bed rooms at our institution, we isolated patients with suspected COVID-19 together with patients without suspected COVID-19 on-site in multiple-bed rooms until SARS-CoV-2-test results were available. We evaluated the likelihood of SARS-CoV-2 transmission to individuals sharing the room with patients isolated on-site. This observational study was performed at the University Hospital Basel, Switzerland, from 03/20 - 11/20. Secondary attack rates were compared between patients hospitalized in multiple-bed rooms and exposed to individuals subjected to on-site isolation precautions (on-site isolation group), and patients exposed to individuals initially not identified as having COVID-19, and not placed under isolation precautions until the diagnosis was suspected (control group). Transmission events were confirmed by whole-genome sequencing. Among 1,218 patients with suspected COVID-19, 67 (5.5%) tested positive for SARS-CoV-2. Of these, 21 were isolated on-site potentially exposing 27 patients sharing the same room. Median contact time was 12 h (interquartile range 7-18 h). SARS-CoV-2 transmission was identified in none of the patients in the on-site isolation group vs. 10/63 (15.9%) in the control group (p = 0.03). Isolation on-site of suspected COVID-19-patients in multiple-bed rooms avoided single-room occupancy and subsequent in-hospital relocation for many patients without confirmed SARS-CoV-2-infection. The absence of secondary transmission among the exposed patients in the on-site isolation group allows for assessment of the risk/benefit ratio of this strategy given the limitation of a small sample size.

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Introduction: Secondary attack rate (SAR) is a proportion of primary contacts developing the diseases within the incubation period upon exposure to a primary case among the total susceptible household contacts. The epidemiological profile and SAR will help in understanding the transmission dynamics of COVID-19 for further strengthening preventive and effective control measures. Objectives of the Study: The study was conducted with the primary objective to estimate the household SAR of COVID-19 cases at Mahisagar District, Gujarat, and to study the epidemiological profile of primary and secondary cases of COVID-19. Methodology: A retrospective study was conducted to estimate SAR among 245 confirmed cases of COVID-19 and 898 susceptible household contacts in Mahisagar district through telephonic interview and questionnaire by the Investigator team. Results: The household SAR was calculated from the current study in Mahisagar district, Gujarat, and was 13.9%. Among primary cases, 74.7% males were affected, and among secondary cases, 52.8% females were affected. The SAR among elderly was 23.9%, and the SAR among children was 3.9%. 74.1% household contacts had developed disease among symptomatic contacts as compared to asymptomatic household contacts. Conclusion: The household SAR in Mahisagar district, Gujarat, was found to be 13.9%. In primary cases, more males, and in secondary cases, more females were found to be affected. The household SAR was increased in elderly as compared to the younger age group. The SAR was more among the contacts of symptomatic cases than asymptomatic cases. Overall hospitalization in public hospitals was more than that in private hospitals.

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BACKGROUND: Quantifying the risk of SARS-CoV-2 transmission in indoor settings is crucial for developing effective non-vaccine prevention strategies and policies. However, summary evidence on the transmission risks in settings other than households, schools, elderly care and healthcare facilities is limited. We conducted a systematic review to estimate the secondary attack rates (SARs) of SARS-CoV-2 and the factors modifying transmission risk in community indoor settings. METHODS: We searched Medline, Scopus, Web of Science, WHO COVID-19 Research Database, MedrXiv, and BiorXiv from January 1, 2020, to February 20, 2023. We included articles with original data for estimating SARS-CoV-2 SARs. We estimated the overall and setting-specific SARs using the inverse variance method for random-effects meta-analyses. RESULTS: We included 34 studies with data on 577 index cases, 898 secondary cases, and 9173 contacts. The pooled SAR for community indoor settings was 20.4% (95% confidence interval [CI] 12.0-32.5%). The setting-specific SARs were highest for singing events (SAR 44.9%, 95% CI 14.5-79.7%), indoor meetings and entertainment venues (31.9%, 10.4-65.3%), and fitness centers (28.9%, 9.9-60.1%). We found no difference in SARs by index case, viral, and setting-specific characteristics. CONCLUSIONS: The risk of SARS-CoV-2 transmission was highest in indoor settings where singing and exercising occurred. Effective mitigation measures such as assessing and improving ventilation should be considered to reduce the risk of transmission in high-risk settings. Future studies should systematically assess and report the host, viral, and setting-specific characteristics that may modify the transmission risks of SARS-CoV-2 and other respiratory viruses in indoor environments.

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BACKGROUND: Comparative data on the transmission of respiratory infections positive and negative for SARS-CoV-2 in households with children are limited. METHODS: In June-August 2020, we recruited 700 participants (175 households, 376 children, 324 adults) to be prospectively followed for all respiratory tract infections. Follow-up lasted from recruitment till April 2022. Daily symptoms were monitored by weekly electronic questionnaires. SARS-CoV-2 PCR testing from nasopharyngeal specimens was performed for symptomatic participants and twice (one-week interval) for the household members of positive participants. Clinical features and secondary attack rates (SARs), based on the onset of symptoms, were compared between SARS-CoV-2-positive and -negative respiratory infections. RESULTS: Most (90%) SARS-CoV-2 infections occurred from January to April 2022 when Omicron BA.1 and BA.2 were the dominant variants. SARS-CoV-2-positive infections were transmitted more often than SARS-CoV-2-negative infections (SAR, 41% vs 24%; P < .001). SARS-CoV-2 transmission was similar for child and adult index cases (SAR, 40% vs 43%; P = .47), but the transmission of SARS-CoV-2-negative infections was higher for child index cases (SAR, 27% vs 18%; P < .001). CONCLUSIONS: Our findings demonstrate that SARS-CoV-2 Omicron viruses spread more effectively within households compared to other respiratory infections.

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BACKGROUND: Households are considered ideal settings for studying the transmission dynamics of an infectious disease. METHODS: A prospective study was conducted, based on the World Health Organization FFX protocol from October 2020 to January,2021. Household contacts of laboratory-confirmed index cases were followed up for their symptomatic history, nasal swabs for RT-PCR,and blood samples for anti-SARS CoV-2 antibodies were collected at enrollment and days 7, 14 and 28. We estimated secondary attack rate (SAR), effective household case cluster size and determinants of secondary infection among susceptible household contacts using multivariable logistic regression. RESULTS: We enrolled 77 index cases and their 543 contacts. Out of these, 252 contacts were susceptible at the time of enrollment. There were 77 household clusters, out of which, transmission took place in 20 (25.9%) giving rise to 34 cases. The acquired secondary attack rate (SAR) was 14.0% (95% CI 9.0-18.0). The effective household case cluster size was 0.46 (95%CI 0.33,0.56). Reported symptoms of nausea and vomiting (aOR, 7.9; 95% CI, 1.4-45.5) and fatigue (aOR, 9.3; 95% CI, 3.8-22.7) were associated with SARS-CoV-2 transmission. CONCLUSIONS: We observed a low SARS-CoV-2 secondary attack rate in the backdrop of high seroprevalence and asymptomatic transmission among households in Karachi, Pakistan.

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The aim of this study was to evaluate the impact of index case vaccination on SARS-CoV-2 transmission to household contacts. In our epidemiological cohort study (May 2022-November 2023), we surveyed registered index case vaccination status and test results for contacts (testing on day 0, and on day 7 for negative contacts) and calculated the secondary attack rate (SAR), i.e., newly infected contacts/susceptible included contacts. The association of the independent variable, index case COVID-19 vaccination (yes/no), with household contact infection was determined using the adjusted odds ratio (aOR) and its 95% confidence interval (CI). We recorded 181 index cases and 314 contacts, of whom 250 agreed to participate; 16 contacts were excluded upon testing positive on day 0. Of the 234 included contacts, 49.1% were women, and the mean (SD) age was 51.9 (19.8) years. The overall SAR of 37.2% (87/234) was lower in the contacts of both vaccinated index cases (34.9% vs. 63.2%; p = 0.014) and index cases with a previous SARS-CoV-2 infection history (27.0% vs. 46.3%; p = 0.002). Index case vaccination showed a protective effect against infection for their household contacts (aOR = 0.21; 95% CI: 0.07, 0.67). The household SAR was high when the Omicron variant circulated. Vaccinated index cases were less likely to transmit SARS-CoV-2 to their contacts.

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OBJECTIVES: This meta-analysis explored secondary infections of SARS-CoV-2 and the effectiveness of non-pharmaceutical interventions (NPIs) in school settings, with the aim of providing a reference to formulate scientific prevention and response strategies for similar major public health emergencies in specific settings. STUDY DESIGN: This was a systematic review and meta-analysis. METHODS: Systematic searches were conducted in PubMed, Web of Science and the Cochrane Library through to 1 August 2022 using the following key search terms: COVID-19, SARS-CoV-2, secondary attack rate, school, transmission, etc. The IVhet model was used for the meta-analysis, and the I2 index and Cochran's Q-test were used to assess heterogeneity. Publication bias was examined using Doi plot, Galbraith plots and Luis Furuya-Kanamori index. Prevalence Critical Appraisal Tool was used to assess the quality of the included articles, while Grading of Recommendations Assessment, Development, and Evaluation was used to rate the quality of the evidence. Subgroup analyses were conducted to explore the potential source of heterogeneity. RESULTS: Thirty-four studies involving 226,727 school contacts and 2216 secondary cases were included in this study. The pooled secondary attack rates (SARs) of close contacts, staff contacts and student contacts were 0.67% (95% confidence interval [CI]: 0.11, 1.56), 0.79% (95% CI: 0.00, 6.72) and 0.50% (95% CI: 0.00, 4.48), respectively. Subgroup analysis suggested that multiple or specific combinations (e.g. the combination of contact restriction and hygiene action) of NPIs appeared to be associated with lower SARs. CONCLUSIONS: The SAR of SARS-CoV-2 was low in schools. Multiple or specific combinations of prevention strategies appear to mitigate SARS-CoV-2 transmission in school settings. These findings provide a basis for continuous improvement of response strategies to major public health emergencies in the school environment.

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BACKGROUND: In California, the 2022 mpox outbreak cumulated 5572 cases, 20% of US cases, as of November 28, 2022; 0.3% of cases were among children <16 years old. The secondary attack rate (SAR) for children sharing households with infected adults is unknown. METHODS: A line list of pediatric mpox household contacts aged <16 years reported through August 31, 2022 was created. It included demographic and clinical information on the contacts. Pediatric contact lists were crossmatched with the state vaccination database to identify those who received postexposure prophylaxis (PEP) with the JYNNEOS vaccine. RESULTS: We identified 129 pediatric household contacts with median age of 7 years (range, 0-15 years). Among 18 symptomatic contacts, 12 (66.7%) underwent mpox testing; 5 (41.2%) were confirmed cases, 6 (50%) were negative, and 1 (0.8%) had an indeterminate result. Six symptomatic children were not tested for mpox (33.3%). Overall, 6 infected contacts were identified, resulting in a SAR of 4.7% (6 of 129). The majority of pediatric household contacts and 4 of 6 infected children identified as Hispanic/Latino. Only 18 children (14%) reported receiving PEP. CONCLUSIONS: The SAR was overall low among pediatric household contacts; none had severe disease. This may be underestimated given low testing rates.

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Background: The ability of SARS-CoV-2 vaccines to protect against infection and onward transmission determines whether immunisation can control global circulation. We estimated the effectiveness of Pfizer-BioNTech mRNA vaccine (BNT162b2) and Oxford AstraZeneca adenovirus vector vaccine (ChAdOx1) vaccines against acquisition and transmission of the Alpha and Delta variants in a prospective household study in England. Methods: Households were recruited based on adult purported index cases testing positive after reverse transcription-quantitative (RT-q)PCR testing of oral-nasal swabs. Purported index cases and their household contacts took oral-nasal swabs on days 1, 3 and 7 after enrolment and a subset of the PCR-positive swabs underwent genomic sequencing conducted on a subset. We used Bayesian logistic regression to infer vaccine effectiveness against acquisition and transmission, adjusted for age, vaccination history and variant. Results: Between 2 February 2021 and 10 September 2021, 213 index cases and 312 contacts were followed up. After excluding households lacking genomic proximity (N=2) or with unlikely serial intervals (N=16), 195 households with 278 contacts remained, of whom 113 (41%) became PCR positive. Delta lineages had 1.53 times the risk (95% Credible Interval: 1.04 - 2.20) of transmission than Alpha; contacts older than 18 years old were 1.48 (1.20 - 1.91) and 1.02 (0.93 - 1.16) times more likely to acquire an Alpha or Delta infection than children. Effectiveness of two doses of BNT162b2 against transmission of Delta was 36% (-1%, 66%) and 49% (18%, 73%) for ChAdOx1, similar to their effectiveness for Alpha. Protection against infection with Alpha was higher than for Delta, 69% (9%, 95%) vs. 18% (-11%, 59%), respectively, for BNT162b2 and 24% (-41%, 72%) vs. 9% (-15%, 42%), respectively, for ChAdOx1. Conclusions: BNT162b2 and ChAdOx1 reduce transmission of the Delta variant from breakthrough infections in the household setting, although their protection against infection within this setting is low.

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BACKGROUND: This study aimed to assess the contact tracing outcomes of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron sub-lineages BA.4, BA.5, and BA.2.75 within Republic of Korea, and to generate foundational data for responding to future novel variants. METHODS: We conducted investigations and contact tracing for 79 confirmed BA.4 cases, 396 confirmed BA.5 cases, and 152 confirmed BA.2.75 cases. These cases were identified through random sampling of both domestically confirmed and imported cases, with the goal of evaluating the pattern of occurrence and transmissibility. RESULTS: We detected 79 instances of Omicron sub-lineage BA.4 across a span of 46 days, 396 instances of Omicron sub-lineage BA.5 in 46 days, and 152 instances of Omicron sub-lineage BA.2.75 over 62 days. One patient with severe illness was confirmed among the BA.5 cases; however, there were no reports of severe illness in the confirmed BA.4 and BA.2.75 cases. The secondary attack risk among household contacts were 19.6% for BA.4, 27.8% for BA.5, and 24.3% for BA.2.75. No statistically significant difference was found between the Omicron sub-lineages. CONCLUSION: BA.2.75 did not demonstrate a higher tendency for transmissibility, disease severity, or secondary attack risk within households when compared to BA.4 and BA.5. We will continue to monitor major SARS-CoV-2 variants, and we plan to enhance the disease control and response systems.

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Background: The coronavirus disease 2019 (COVID-19) pandemic has reached a staggering number of almost 280 million cases worldwide, with over 5.4 million deaths as of 29 December 2021. A further understanding of the factors related to the household spread of the infection might help to bring about specific protocols to curb such transmission. Objective: This study aims to find the secondary attack rate (SAR) and factors affecting SAR among the households of mild COVID-19 cases. Methods: An observational study was designed where data of patients admitted at All India Institute of Medical Sciences, New Delhi due to mild COVID-19 were collected, and outcome was noted after the discharge of the patient. Index cases who were the first in the household to have a positive infection only were included. Based on these data, the overall household SAR, factors related to the index case and contacts that affected transmissibility were noted. Results: A total of 60 index cases having contacts with 184 household members were included in the present study. The household SAR was measured to be 41.85%. At least one positive case was present in 51.67% households. Children below 18 years old had lower odds of getting a secondary infection compared to adults and elderly [odds ratio (OR) = 0.46, 95%CI = 0.22-0.94, p = 0.0383). An exposure period of more than a week was significantly associated with a higher risk of infection (p = 0.029). The rate of transmissibility drastically declined with effective quarantine measures adopted by the index case (OR = 0.13, 95%CI = 0.06-0.26, p < 0.00001). Symptomatic index cases contributed more to the SAR than asymptomatic primaries (OR = 4.74, 95%CI = 1.03-21.82, P = 0.045). Healthcare worker index cases had lower rates of spread (OR = 0.29, 95%CI = 0.15-0.58, P = 0.0003). Conclusion: The high SAR shows the household is a potential high-risk unit for transmissibility of COVID-19. Proper quarantine measures of all those exposed to the index case can mitigate such spread and lead to reduction of risk of COVID-19 within a household.

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Objective: The aim of this study was to observe the secondary infection rate and transmission dynamics of COVID-19 among household contacts, and their associations with various factors across four dimensions of interaction. Methods: This was a case-ascertained study among unvaccinated household contacts of a laboratory-confirmed COVID-19 case in New Delhi between December 2020 and July 2021. For this study, 99 index cases and their 316 household contacts were interviewed and sampled (blood and oro-nasal swab) on days 1, 7, 14, and 28. Results: The secondary infection rate among unvaccinated household contacts was 44.6% (95% confidence interval (CI) 39.1-50.1). The predictors of secondary infection among individual contact levels were: being female (odds ratio (OR) 2.13), increasing age (OR 1.01), symptoms at baseline (OR 3.39), and symptoms during follow-up (OR 3.18). Among index cases, age of the primary case (OR 1.03) and symptoms during follow-up (OR 6.29) were significantly associated with secondary infection. Among household-level and contact patterns, having more rooms (OR 4.44) and taking care of the index case (OR 2.02) were significantly associated with secondary infection. Conclusion: A high secondary infection rate highlights the need to adopt strict measures and advocate COVID-19-appropriate behaviors. A targeted approach for higher-risk household contacts would efficiently limit infections among susceptible contacts.

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BACKGROUND: The impact of infection-induced immunity on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission has not been well established. Here we estimate the effects of prior infection induced immunity in adults and children on SARS-CoV-2 transmission in households. METHODS: We conducted a household cohort study from March 2020-November 2022 in Managua, Nicaragua; following a housheold SARS-CoV-2 infection, household members are closely monitored for infection. We estimate the association of time period, age, symptoms, and prior infection with secondary attack risk. RESULTS: Overall, transmission occurred in 70.2% of households, 40.9% of household contacts were infected, and the secondary attack risk ranged from 8.1% to 13.9% depending on the time period. Symptomatic infected individuals were more infectious (rate ratio [RR] 21.2, 95% confidence interval [CI]: 7.4-60.7) and participants with a prior infection were half as likely to be infected compared to naïve individuals (RR 0.52, 95% CI:.38-.70). In models stratified by age, prior infection was associated with decreased infectivity in adults and adolescents (secondary attack risk [SAR] 12.3, 95% CI: 10.3, 14.8 vs 17.5, 95% CI: 14.8, 20.7). However, although young children were less likely to transmit, neither prior infection nor symptom presentation was associated with infectivity. During the Omicron era, infection-induced immunity remained protective against infection. CONCLUSIONS: Infection-induced immunity is associated with decreased infectivity for adults and adolescents. Although young children are less infectious, prior infection and asymptomatic presentation did not reduce their infectivity as was seen in adults. As SARS-CoV-2 transitions to endemicity, children may become more important in transmission dynamics.

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BACKGROUND: The impact of children on the transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) remains uncertain. This study provides an insight into distinct patterns of SARS-CoV-2 household transmission in case of pediatric and adult index cases as well as age-dependent susceptibility to SARS-CoV-2 infection. METHODS: Immune analysis, medical interviewing, and contact tracing of 26 families with confirmed SARS-CoV-2 infection cases have been conducted. Blood samples were analyzed serologically with the use of a SARS-CoV-2-specific IgG assay and virus neutralization test (VNT). Uni- and multivariable linear regression and mixed effect logistic regression models were used to describe potential risk factors for higher contagiousness and susceptibility to SARS-CoV-2 infection. RESULTS: SARS-CoV-2 infection could be confirmed in 67 of 124 family members. Fourteen children and 11 adults could be defined as index cases in their households. Forty of 82 exposed family members were defined as secondarily infected. The mean secondary attack rate in households was 0.48 and was significantly higher in households with adult than with pediatric index cases (0.85 vs 0.19; p < 0.0001). The age (grouped into child and adult) of index case, severity of disease, and occurrence of lower respiratory symptoms in index cases were significantly associated with secondary transmission rates in households. Children seem to be equally susceptible to acquire a SARS-CoV-2 infection as adults, but they suffer milder courses of the disease or remain asymptomatic. CONCLUSION: SARS-CoV-2 transmission from infected children to other household members occurred rarely in the first wave of the pandemic, despite close physical contact and the lack of hygienic measures.

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Background: Accurate estimation of household secondary attack rate (SAR) is crucial to understand the transmissibility of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The impact of population-level factors, such as transmission intensity in the community, on SAR estimates is rarely explored. Methods: In this study, we included articles with original data to compute the household SAR. To determine the impact of transmission intensity in the community on household SAR estimates, we explored the association between SAR estimates and the incidence rate of cases by country during the study period. Results: We identified 163 studies to extract data on SARs from 326 031 cases and 2 009 859 household contacts. The correlation between the incidence rate of cases during the study period and SAR estimates was 0.37 (95% CI, 0.24-0.49). We found that doubling the incidence rate of cases during the study period was associated with a 1.2% (95% CI, 0.5%-1.8%) higher household SAR. Conclusions: Our findings suggest that the incidence rate of cases during the study period is associated with higher SAR. Ignoring this factor may overestimate SARs, especially for regions with high incidences, which further impacts control policies and epidemiological characterization of emerging variants.

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BACKGROUND: Asymptomatic COVID-19 cases have complicated the surveillance and tracking of the pandemic. Previous studies have estimated that 15-25% of all infectees remain asymptomatic. METHODS: Based on contact tracing data from Oslo, Norway, we estimated transmission and susceptibility dynamics among symptomatic and asymptomatic cases and their contacts as identified by manual contact tracing between September 1, 2020, and September 1, 2021. RESULTS: Among 27,473 indexes and 164,153 registered contacts, the secondary attack rate (SAR-14) was estimated to be 28% lower through asymptomatic exposure (13%) compared to symptomatic exposure (18%). Furthermore, those infected by asymptomatic cases were almost three times more likely to be asymptomatic compared to those infected by symptomatic cases. CONCLUSIONS: Symptomatic cases spread the virus to a greater extent than asymptomatic, and infectees are more likely to be asymptomatic if their assumed infector was asymptomatic.

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Since May 2022, a large number of monkeypox cases have been reported in Europe, the United States, and other nonendemic settings. Taking into account the strict measures implemented due to the coronavirus disease 2019 pandemic and the desire of people to reclaim what is perceived as lost time, mass gatherings this summer were highly attended. Based on data for the secondary attack rate among unvaccinated contacts from endemic countries, we estimate that, on average, >1 secondary case is anticipated per infectious person if he/she has a high number of group contacts (>30) or >8 close contacts. Although the role of group contacts in mass gatherings is uncertain (less likely to involve physical contact, shorter duration), close contacts associated with the event (eg, intimate/sexual contact with other attendees) might be the amplifying event. Enforcing awareness, early recognition, and engaging affected populations in the monkeypox response are important to control transmission.

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Introduction: The COVID-19 epidemic is fast-evolving and restrictions to contain it changes quickly. The secondary attack rate (SAR) indicates the infectiousness at the household level, and it provides a clue of load of infections in the community. Rapid implementation of a large scale, but brief survey provides a nationally representative view of the pandemic's progression and impact as well as the effect of the measures taken to control the spread. Materials and Methods: This cross-sectional study was done for a period of 2 months July-August 2020, in one of the rural health and demographic surveillance system (HDSS) site in India among 11,507 households having 46,571 individuals with the objective to determine the prevalence of the COVID-19 infection and to estimate the family SAR. The data were collected using the mobile phone by calling the head of the households registered under the HDSS. The research tool was created using questions based on the guidelines provided by the Ministry of Health and Family Welfare, India. The interviewers were first trained in data collection. Results: The households of 33,780 individuals were contacted and 33 patients were diagnosed as COVID positive, prevalence rate of 0.1% was thus documented through telephonic survey. The mean age of COVID patients was found to be 37 ± 16 years, and 63% of the diagnosed patients were males, majority of them belonged to above poverty line households. During the survey, 46 individuals reported to have the symptoms suggestive of COVID, fever and cough were the most commonly reported symptoms. The family SAR of 17.2% was documented. Conclusion: Thus to conclude a low COVID-19 prevalence rate of 0.1%, a higher family SAR of 17.2% was reported in the current study. Timely diagnosis and quarantine of close contacts should be continued to be implemented rigorously to prevent the spread of the COVID-19 virus. These efforts will be useful to contain the epidemic before it reaches an alarming level in the rural areas.

Résumé Introduction: L'épidémie de COVID-19 évolue rapidement et les restrictions pour la contenir changent rapidement. Le taux d'attaque secondaire (SAR) indique l'infectiosité au niveau du ménage et fournit un indice de la charge d'infections dans la communauté. La mise en œuvre rapide d'une enquête à grande échelle mais brève fournit une vue représentative à l'échelle nationale de la progression et de l'impact de la pandémie ainsi que de l'effet des mesures prises pour contrôler la propagation. Matériels et Méthodes: cette étude transversale a été réalisée sur une période de 2 mois de juillet à août 2020, dans l'un des sites du système de surveillance sanitaire et démographique en milieu rural (HDSS) en Inde auprès de 11 507 ménages comptant 46 571 individus dans le but de déterminer prévalence de l'infection au COVID-19 et d'estimer le DAS familial. Les données ont été collectées à l'aide du téléphone mobile en appelant le chef de ménage inscrit au HDSS. L'outil de recherche a été créé à l'aide de questions basées sur les directives fournies par le ministère indien de la Santé et du Bien-être familial. Les enquêteurs ont d'abord été formés à la collecte de données. Résultats: les ménages de 33 780 individus ont été contactés et 33 patients ont été diagnostiqués positifs au COVID, un taux de prévalence de 0,1 % a ainsi été documenté par une enquête téléphonique. L'âge moyen des patients COVID était de 37 ± 16 ans, et 63 % des patients diagnostiqués étaient des hommes, la majorité d'entre eux appartenant à des ménages au-dessus du seuil de pauvreté. Au cours de l'enquête, 46 personnes ont déclaré avoir des symptômes évocateurs de COVID, la fièvre et la toux étaient les symptômes les plus fréquemment signalés. Le SAR familial de 17,2 % a été documenté. Conclusion: Ainsi, pour conclure à un faible taux de prévalence de la COVID-19 de 0,1 %, un DAS familial supérieur de 17,2 % a été rapporté dans la présente étude. Le diagnostic rapide et la mise en quarantaine des contacts étroits doivent être poursuivis et mis en œuvre de manière rigoureuse pour empêcher la propagation du virus COVID-19. Ces efforts seront utiles pour contenir l'épidémie avant qu'elle n'atteigne un niveau alarmant dans les zones rurales. Mots-clés: COVID 19, système de surveillance sanitaire et démographique, téléphone portable, prévalence, milieu rural, taux d'attaque secondaire.

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BACKGROUND: The transmission and fatal risk of severe fever with thrombocytopenia syndrome (SFTS), an emerging infectious disease first discovered in China in 2009, still needed further quantification. This research aimed to analyze the SFTS clusters and assess the transmission and mortality risk for SFTS. METHODS: Both epidemiological investigation and case reports regarding SFTS clusters in China during 2011-2021 were obtained from the Public Health Emergency Information Management System of the Chinese Center for Disease Control and Prevention Information System. The transmission risk was evaluated by using the secondary attack rate (SAR) and relative risk (RR). Mortality risk factors were analyzed using a logistic regression model. RESULTS: There were 35 SFTS clusters during 2011-2021 involving 118 patients with a fatality rate of 22.0%. The number of clusters annually increased seasonally from April to September. The clusters mainly occurred in Anhui (16 clusters) and Shandong provinces (8 clusters). The SAR through contact with blood or bloody fluids was much higher than that through contact with non-bloody fluids (50.6% vs 3.0%; χ2 = 210.97, P < 0.05), with an RR of 16.61 [95% confidence interval (CI): 10.23-26.97]. There was a statistically significant difference in the SAR between exposure to the blood of a deceased person during burial preparation and exposure to the living patients' blood (66.7% vs 34.5%; χ2 = 6.40, P < 0.05), with an RR of 1.93 (95% CI: 1.11-3.37). The mortality risk factors were a long interval from onset to diagnosis [odds ratio (OR) = 1.385), 95% CI: 1.083-1.772, P = 0.009) and advanced age (OR: 1.095, 95% CI: 1.031-1.163, P = 0.01). CONCLUSIONS: The SFTS clusters showed a high mortality rate and resulted in a high SAR. Contact with a bleeding corpse was associated with a higher infection risk, compared with contacting the blood from living patients. It is important to promote early detection and appropriate case management of patients with SFTS, as well as improved handling of their corpses, to prevent further transmission and mortality.

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