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Travel-Associated H1N1 Influenza in Singapore

Airport thermal scanners detected only 12% of travel-associated flu cases; many travelers boarded flights despite symptoms.

Travelers play a key role in spreading many infections, including influenza. Such was the case with the spread of 2009 H1N1 influenza to Singapore, a major travel hub serving 37 million air passengers annually.

Before the 2009 H1N1 virus entered Singapore, public health officials implemented a containment plan, in which all passengers arriving at the international airport underwent thermal scanning, and all passengers with influenza-like illness (ILI) were referred to a designated screening center (Tan Tock Seng Hospital [TTSH]) for treatment and isolation. In this report, investigators described the first 116 patients hospitalized at TTSH with travel-associated H1N1 infection. By definition, all patients arrived in Singapore during the containment phase of the epidemic, developed ILI within 10 days of arrival, and had H1N1 influenza confirmed via real-time reverse-transcriptase PCR on respiratory samples.

The first patient arrived in Singapore on May 26, 2009, and the others followed over a 5-week period. During the first 2 weeks, most patients had acquired their infections in the U.S., but the origin of exposure shifted rapidly to Australasia and Southeast Asia. The mean age of patients was 29, and half were Singaporean. One quarter of patients were symptomatic when they boarded flights; 15% developed symptoms during travel. Airport thermal scanners detected only 12% of patients overall and only 40% of those with symptomatic infection on arrival. At the time of evaluation, only 61% of patients had fevers high enough to meet CDC criteria for ILI, and 54% had fevers that met the WHO criteria.

Comment: This analysis shows the dynamic nature of travel-associated infection and the challenges of dealing with introduction and spread of infection, even in a place with good surveillance and infrastructure. The authors question whether exit screening at the time of trip origin would be useful in identifying travelers who are ill. Existing strategies clearly do not stop international spread of influenza.

— Mary E. Wilson, MD

Published in Journal Watch Infectious Diseases December 16, 2009

Citation(s):

Mukherjee P et al. Epidemiology of travel-associated pandemic (H1N1) 2009 infection in 116 patients, Singapore. Emerg Infect Dis 2010 Jan; [e-pub ahead of print]. (http://www.cdc.gov/eid/content/16/1/pdfs/09-1376.pdf)

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• H1N1
  nick dalton, 23 Dec 2009 2:31 PM EST
  I don't get people like that! Don't you think about the people you may infect? I advise us all to... [more]

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