# 3690
Incredibly, in 2009 we are still studying and debating the basics of the science behind influenza. We don’t know with certainty, for instance, the exact mechanisms of how it is transmitted.
Is it aerosolized (airborne) transmission? Or mainly spread through large Droplets? What role does contact with contaminated fomites (inanimate objects like keyboards, phones, doorknobs . . .) play?
The assumption over the years has been that influenza is largely transmitted by large droplets through coughs of sneezes . . . but good science to back that up is scant.
Today we get a study in the CDC’s Journal of Emerging Infectious Diseases that may help answer some of these questions:
Han K, Zhu X, He F, Liu L, Zhang L, Ma H, et al. Lack of airborne transmission during outbreak of pandemic (H1N1) 2009 among tour group members, China, June 2009. Emerg Infect Dis. 2009 Oct; [Epub ahead of print]
Briefly, an American tourist in China spread the novel H1N1 virus to fellow passengers by talking, at close range for 2 minutes or more. Contacts who spoke with her for 10 minutes or more were 5 times more likely to contract the flu than those with only 2 minutes of contact.
Passengers who didn’t speak to her, but were in relatively close proximity (sharing transportation, dining at the same table, etc) didn’t catch the virus.
Leading researchers to believe that this virus is primarily transmitted at close range through large droplets expelled while talking, coughing, or sneezing.
Jason Gale of Bloomberg news picks up the story.
Tourist in China Spread Swine Flu While Talking, Study Says
By Jason Gale
Aug. 31 (Bloomberg) -- An American tourist in China spread swine flu while talking to fellow bus passengers at close range, suggesting that virus-laden droplets expelled from the mouth are a key mode of transmission, scientists found.
The 40-year-old woman who traveled in early June from New York to Jiuzhaigou, a popular tourist spot in southwestern China, probably sparked an outbreak among 30 members of her holiday group, the researchers said in a study in the October edition of the journal Emerging Infectious Diseases.
The woman developed symptoms about a day after leaving the U.S. and spent almost 7 hours riding with the group on an air- conditioned bus. Those who chatted with her for at least 10 minutes within a 2-meter (6.6-foot) range, regardless of their seat or other forms of social contact, had a greater risk of infection, the authors said. The finding suggests preventing transmission by droplets may foil the spread of the pandemic bug.
From the EID study (slightly reformatted for readability), just a few excerpts to give you some idea of how these conclusions were reached.
The index case-patient began having chills at ≈9:00 PM during her flight from Hong Kong to Chengdu. She started coughing before she boarded the flight from Chengdu to Jiuzhaigou on June 3 and continued to cough during the entire tour and after she returned to Chengdu.
She had extensive interactions with other members of the group, who talked with each other, helped each other take pictures, gave chewing gum to each other, had group meals together, and stayed in the same hotel. During the 3-day trip, the group traveled together in an air-conditioned tour bus; doors were shut and windows were sealed to conserve energy.
While traveling among the various tourist attractions, the group was together on bus rides for a total of 6 hours and 50 minutes. When we evaluated the contact patterns of the tour group with the index case-patient, we found that for the 16 tourists who had talked with the index case-patient from close range (<2 m) for >2 minutes, the attack rate was 56%, whereas none of the 14 tourists who did not talk with her became ill.
Members of the tour group who had talked with the index case-patient for >10 minutes were almost 5× as likely to become ill than those who had talked with her for 2–9 minutes (Table 2). The 14 passengers who had not talked with the index case-patient did report other interactions with her, such as dining at the same table, sitting within 2 rows on the same flight or bus ride, and receiving chewing gum from her. Moreover, 3 of these 14 uninfected passengers had sat within 2 seats of the index case-patient during the bus rides but had never talked with her from close range.
Among the conclusions of this study:
The role of airborne transmission for influenza is debatable (7–10). Our investigation did not find evidence of airborne transmission during this outbreak. The lack of cases among 14 tourists who were with the index case-patient in an enclosed bus cabin for nearly 7 hours suggests that airborne transmission was not a factor.
In conclusion, this outbreak of influenza A pandemic (H1N1) 2009 virus infection was caused by transmission during coughing or vocalization by an imported case-patient. The virus spread by droplet transmission when the index case-patient was talking with her fellow tourists.
The findings of our investigation highlight the importance of preventing droplet transmission during a pandemic.
A fascinating study, and one that gives us some insight into how this novel H1N1 virus is currently transmitted. This is not likely to be the final word, however, on influenza transmission.
The good news here is that it appears that avoiding direct, close, and prolonged face-to-face contact with infected individuals greatly reduces the chances of infection.
Other measures, such as hand hygiene, and the use of facemasks and respirators (where appropriate), likely further reduce the risk.
Of course, we don’t have good studies on that, either.
