Abstract
During June 2-8, 2009, an outbreak of influenza A pandemic (H1N1) 2009 occurred among 31 members of a tour group in China. To identify the mode of transmission and risk factors, we conducted a retrospective cohort investigation. The index case-patient was a female tourist from the United States. Secondary cases developed in 9 (30%) tour group members who had talked with the index case-patient and in 1 airline passenger (not a tour group member) who had sat within 2 rows of her. None of the 14 tour group members who had not talked with the index case-patient became ill. This outbreak was apparently caused by droplet transmission during coughing or talking. That airborne transmission was not a factor is supported by lack of secondary cases among fellow bus and air travelers. Our findings highlight the need to prevent transmission by droplets and fomites during a pandemic.
Highlights
Start of the 2009 influenza pandemic [4]
During June 2–8, 2009, an outbreak of pandemic (H1N1) 2009 occurred among members of a tour group. We investigated this outbreak to identify the source of infection, mode of transmission, and risk factors for infection
Since the emergence of a novel influenza A (H1N1) virus in early 2009 in Mexico [1,2], the virus has spread to 156 countries, territories, and areas; as of July 27, 2009, a total of 134,503 laboratory-confirmed cases and 816 deaths had been reported [3]
Summary
Investigations of transmission chains early in the pandemic will add to our understanding of the special characteristics of this new virus, including whether its mode of transmission differs from that of seasonal influenza viruses. This information will be useful for effective control of the spread of this virus. On June 11, 2009, the World Health Organization declared that the world was experiencing the Author affiliations: Chinese Center for Disease Control and Prevention, Beijing, People’s Republic of China Zhu); Guangdong Center for Disease Control and Prevention, Guangzhou, People’s Republic of China Han); Zhejiang Center for Disease Control and Prevention, Hangzhou, People’s Republic of China
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