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2009 H1N1 Influenza in a Tour Group in China

Influenza developed in 30% of tour members who had talked with an H1N1-infected woman in the group but in none who had not.

An outbreak of 2009 H1N1 influenza in a tour group in China during June 2009 provided an opportunity to assess spread during travel. The index case-patient, a 40-year-old woman, developed symptoms 23 hours after leaving the U.S. and just before arrival in Chengdu, China, from Hong Kong. Over the next 3 days, she flew to Jiuzhaigou and traveled with 30 other tour group members. The diagnosis of 2009 H1N1 influenza was made after she returned to Chengdu.

Chinese health authorities placed the tour members under involuntary medical observation and isolated those with symptoms or laboratory evidence of infection. They contacted all passengers on the flights originating in Hong Kong, Chengdu, and Jiuzhaigou and obtained detailed information about activities of the tour members during their 3 days together. They collected daily throat-swab specimens from all the tour members and from other passengers who had shared any of the same flights and were symptomatic. Infection was confirmed with real-time reverse-transcriptase PCR.

Infection with 2009 H1N1 virus was confirmed in nine additional tour members (30%) and in another person who had sat two rows behind the index case-patient on a flight. All the tour members who became ill had talked with the index case-patient. Among the 16 who had talked with her at close range (<2 m) for 2 minutes, 56% became ill. Despite almost 7 hours of travel together in an air-conditioned tour bus, members who had not had face-to-face conversations with the index case-patient did not become ill. The secondary attack rate was 41% among those aged 18 to 39 and 21% among those aged 40 to 63.

Comment: The findings in this outbreak are consistent with droplet or fomite transmission. Airborne transmission was not documented despite shared environments on the planes and buses. All aircraft used by the index case-patient had high-efficiency particulate air filters, and less than half the air was recirculated. Whether more-extensive spread would have occurred in the absence of good ventilation and filtered air remains unclear.

— Mary E. Wilson, MD

Published in Journal Watch Infectious Diseases October 14, 2009

Citation(s):

Han K et al. Lack of airborne transmission during outbreak of pandemic (H1N1) 2009 among tour group members, China, June 2009. Emerg Infect Dis 2009 Oct; 15:1578.

• Medline abstract (Free)