Influenza in the Tropics: The Role of Humidity

Liat Vaisenberg, University of California, Irvine

To test hypotheses of the seasonality of influenza, we analyze the pairwise comovements of the incidence of influenza and malaria, and of influenza and chickenpox, in the tropical country of Burundi. We use the Goodman-Grunfeld nonparametric test for comovement between two time series, correcting for serial correlation. We find a significant comovement between influenza and malaria, suggesting that humidity, an important factor in the transmission of malaria, also plays a role in influenza transmission, at least in the tropics. No comovement was found between influenza and chickenpox, implying that crowding effects are not a significant factor in the seasonality of influenza in the tropics. We show that an indirect method may provide information that would otherwise elude direct analysis. Our data suggest that either the driving factors of cyclicality, or modes of influenza transmission, or both, may work differently in the tropics than in temperate regions.