Measles transmission during commercial air travel in Brazil

Airborne disease transmission during commercial air travel has been recently highlighted by the transmission of severe acute respiratory syndrome (SARS) to as many as 25 passengers in 2003 (Olsen et al., 2003, WHO, 2003) and by the risk of influenza H5N1 transmission, if person-to-person transmission became more common (Ozonoff and Pepper, 2005). Measles transmission aboard aircrafts, however, is believed to be uncommon (Amornkul et al., 2004, Mangili and Gendreau, 2005). A recent review found only three case studies describing measles transmission during commercial air travel; all in the United States (Amler et al., 1982, CDC, 1983, CDC, 2004, Mangili and Gendreau, 2005). We report the transmission of measles infection on an airplane that led to two secondary confirmed measles cases in Brazil in 2005.

In June 2005, an unvaccinated 36-year-old surfer was identified as the initial case of a measles outbreak in Brazil. This outbreak resulted in a total of six confirmed cases identified through passive and active surveillance (PAHO, 2005). As part of the outbreak control measures, 73,282 persons were vaccinated. This initial case was exposed to a confirmed measles outbreak in the Maldives during a surfing tournament. During the periods of incubation and communicability, this person traveled by air on international flights before arriving to Brazil and on five domestic flights within Brazil. Two secondary infections among fellow passengers traveling between São Paulo and Florianópolis on 17 June (1 day before the rash onset of the index passenger) were confirmed by viral isolation and serology. One of these secondary cases was an unvaccinated 38-year-old man with rash onset on 1st July, and the other was an unvaccinated 5-year-old child with rash onset on 3rd July. The child had not been vaccinated due to alternative medical practices. According to their boarding passes, the index passenger was in seat 8-A and the secondary cases in seats 5-K and 16-A. Of the 334 passengers traveling with this index passenger during his period of communicability, 118 were contacted and investigated. No other secondary cases were identified. The epidemiologic investigation suggests that transmission may have occurred towards the end of the period of communicability of the index passenger.

Reports of measles transmission aboard aircrafts are infrequent and transmission may well be affected by the type of aircraft and the ventilation and filtration systems used. A higher proportion of large commercial aircraft than smaller planes use high efficiency particulate air (HEPA) filters (Mangili and Gendreau, 2005). Nevertheless, our experience may suggest that airplane-associated transmission is underreported in the scientific literature. Transmission of indigenous measles has been interrupted in the Region of the Americas, but cases related to importations from other regions of the world continue to occur (PAHO, 2005). As highlighted in this report, measles transmission during commercial air travel represents an important challenge to health authorities due to the large number of persons potentially exposed and the difficulties in tracing them. However, these authorities should be aware that secondary measles transmission to fellow passengers does occur. Therefore, measles persons-cases should be asked about history of air travel and fellow passengers subsequently contacted and investigated as part of the standard response to a measles case in countries with disease elimination goals.