Low transmission rate of 2009 H1N1 Influenza during a long-distance bus trip

BACKGROUND: Current data on the risk of transmission of 2009 H1N1 Influenza in public transportation systems (e.g., public trains, busses, airplanes) are conflicting. The main transmission route of this virus is thought to be via droplets, but airborne transmission has not been completely ruled out. METHODS: This is a contact tracing investigation of a young woman subsequently diagnosed with the 2009 H1N1 Influenza virus who was symptomatic during a long-distance bus trip from Spain to Switzerland. Fever and cough had begun 24 h earlier, 2 h before she stepped onto a bus for a long-distance trip. After the 2009 H1N1 virus had been confirmed in the patient, the other bus travellers were contacted by telephone on day 7 and 10 after the bus trip. RESULTS: Of the 72 individuals travelling on the bus with the H1N1-infected young woman, 52 (72%) could be contacted. Only one of these 52 developed fever, with onset of symptoms 3 days after the bus trip, and rRT-PCR analysis of the nasopharyngeal swab showed the infection to be caused by the 2009 H1N1 virus. One other person complained of coughing 1 day after the bus trip, but without fever, and no further investigation was carried out. All other passengers remained without fever, coughing, or arthralgia. The risk of transmission was calculated as 1.96% (95% confidence interval 0–5.76%). CONCLUSION: The transmission rate of 2009 H1N1 Influenza was low on a long-distance bus trip. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s15010-011-0084-x) contains supplementary material, which is available to authorized users.