Giuseppe
Emeritus
[Source: PLoS ONE, full text: (LINK). Abstract, edited.]
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Influenza Transmission in a Community during a Seasonal Influenza A(H3N2) Outbreak (2010?2011) in Mongolia: A Community-Based Prospective Cohort Study
Nao Nukiwa-Souma<SUP>1</SUP>, Alexanderyn Burmaa<SUP>2</SUP>, Taro Kamigaki<SUP>1</SUP>, Ishiin Od<SUP>3</SUP>, Namuutsetsegiin Bayasgalan<SUP>2</SUP>, Badarchiin Darmaa<SUP>2</SUP>, Akira Suzuki<SUP>1</SUP>, Pagbajabyn Nymadawa<SUP>2</SUP><SUP>,</SUP><SUP>4</SUP>, Hitoshi Oshitani<SUP>1</SUP><SUP>*</SUP>
1 Department of Virology, Tohoku University Graduate School of Medicine, Sendai, Japan, 2 National Influenza Center, National Center of Communicable Diseases, Ulaanbaatar, Mongolia, 3 Baganuur District, Ulaanbaatar, Mongolia, 4 Mongolian Academy of Medical Sciences, Ulaanbaatar, Mongolia
Abstract
Background
Knowledge of how influenza viruses spread in a community is important for planning and implementation of effective interventions, including social distancing measures. Households and schools are implicated as the major sites for influenza virus transmission. However, the overall picture of community transmission is not well defined during actual outbreaks. We conducted a community-based prospective cohort study to describe the transmission characteristics of influenza in Mongolia.
Methods and Findings
A total of 5,655 residents in 1,343 households were included in this cohort study. An active search for cases of influenza-like illness (ILI) was performed between October 2010 and April 2011. Data collected during a community outbreak of influenza A(H3N2) were analyzed. Total 282 ILI cases occurred during this period, and 73% of the subjects were aged <15 years. The highest attack rate (20.4%) was in those aged 1?4 years, whereas the attack rate in those aged 5?9 years was 10.8%. Fifty-one secondary cases occurred among 900 household contacts from 43 households (43 index cases), giving an overall crude household secondary attack rate (SAR) of 5.7%. SAR was significantly higher in younger household contacts (relative risk for those aged <1 year: 9.90, 1?4 years: 5.59, and 5?9 years: 6.43). We analyzed the transmission patterns among households and a community and repeated transmissions were detected between households, preschools, and schools. Children aged 1?4 years played an important role in influenza transmission in households and in the community at large. Working-age adults were also a source of influenza in households, whereas elderly cases (aged ≥65 years) had no link with household transmission.
Conclusions
Repeated transmissions between households, preschools, and schools were observed during an influenza A(H3N2) outbreak period in Mongolia, where subjects aged 1?4 years played an important role in influenza transmission.
Citation: Nukiwa-Souma N, Burmaa A, Kamigaki T, Od I, Bayasgalan N, et al. (2012) Influenza Transmission in a Community during a Seasonal Influenza A(H3N2) Outbreak (2010?2011) in Mongolia: A Community-Based Prospective Cohort Study. PLoS ONE 7(3): e33046. doi:10.1371/journal.pone.0033046
Editor: Benjamin J. Cowling, University of Hong Kong, Hong Kong
Received: November 18, 2011; Accepted: February 9, 2012; Published: March 13, 2012
Copyright: ? 2012 Nukiwa-Souma et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This study was supported by Grant-in-Aid for Scientific Research (C), grant number 20603001. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
* E-mail: oshitanih@med.tohoku.ac.jp
-Nao Nukiwa-Souma<SUP>1</SUP>, Alexanderyn Burmaa<SUP>2</SUP>, Taro Kamigaki<SUP>1</SUP>, Ishiin Od<SUP>3</SUP>, Namuutsetsegiin Bayasgalan<SUP>2</SUP>, Badarchiin Darmaa<SUP>2</SUP>, Akira Suzuki<SUP>1</SUP>, Pagbajabyn Nymadawa<SUP>2</SUP><SUP>,</SUP><SUP>4</SUP>, Hitoshi Oshitani<SUP>1</SUP><SUP>*</SUP>
1 Department of Virology, Tohoku University Graduate School of Medicine, Sendai, Japan, 2 National Influenza Center, National Center of Communicable Diseases, Ulaanbaatar, Mongolia, 3 Baganuur District, Ulaanbaatar, Mongolia, 4 Mongolian Academy of Medical Sciences, Ulaanbaatar, Mongolia
Abstract
Background
Knowledge of how influenza viruses spread in a community is important for planning and implementation of effective interventions, including social distancing measures. Households and schools are implicated as the major sites for influenza virus transmission. However, the overall picture of community transmission is not well defined during actual outbreaks. We conducted a community-based prospective cohort study to describe the transmission characteristics of influenza in Mongolia.
Methods and Findings
A total of 5,655 residents in 1,343 households were included in this cohort study. An active search for cases of influenza-like illness (ILI) was performed between October 2010 and April 2011. Data collected during a community outbreak of influenza A(H3N2) were analyzed. Total 282 ILI cases occurred during this period, and 73% of the subjects were aged <15 years. The highest attack rate (20.4%) was in those aged 1?4 years, whereas the attack rate in those aged 5?9 years was 10.8%. Fifty-one secondary cases occurred among 900 household contacts from 43 households (43 index cases), giving an overall crude household secondary attack rate (SAR) of 5.7%. SAR was significantly higher in younger household contacts (relative risk for those aged <1 year: 9.90, 1?4 years: 5.59, and 5?9 years: 6.43). We analyzed the transmission patterns among households and a community and repeated transmissions were detected between households, preschools, and schools. Children aged 1?4 years played an important role in influenza transmission in households and in the community at large. Working-age adults were also a source of influenza in households, whereas elderly cases (aged ≥65 years) had no link with household transmission.
Conclusions
Repeated transmissions between households, preschools, and schools were observed during an influenza A(H3N2) outbreak period in Mongolia, where subjects aged 1?4 years played an important role in influenza transmission.
Citation: Nukiwa-Souma N, Burmaa A, Kamigaki T, Od I, Bayasgalan N, et al. (2012) Influenza Transmission in a Community during a Seasonal Influenza A(H3N2) Outbreak (2010?2011) in Mongolia: A Community-Based Prospective Cohort Study. PLoS ONE 7(3): e33046. doi:10.1371/journal.pone.0033046
Editor: Benjamin J. Cowling, University of Hong Kong, Hong Kong
Received: November 18, 2011; Accepted: February 9, 2012; Published: March 13, 2012
Copyright: ? 2012 Nukiwa-Souma et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This study was supported by Grant-in-Aid for Scientific Research (C), grant number 20603001. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
* E-mail: oshitanih@med.tohoku.ac.jp
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