Abstract
BackgroundInformation on the timing of influenza circulation remains scarce in Tropical regions of Africa.ObjectivesWe assessed the relationship between influenza activity and several meteorological factors (temperature, specific humidity, precipitation) and characterized the timing of influenza circulation and its implications to vaccination strategies in Kenya.MethodsWe analyzed virologically confirmed influenza data for outpatient influenza‐like illness (ILI), hospitalized for severe acute respiratory infections (SARI), and cases of severe pneumonia over the period 2007–2013. Using logistic and negative binomial regression methods, we assessed the independent association between climatic variables (lagged up to 4 weeks) and influenza activity.ResultsThere were multiple influenza epidemics occurring each year and lasting a median duration of 2–4 months. On average, there were two epidemics occurring each year in most of the regions in Kenya, with the first epidemic occurring between the months of February and March and the second one between July and November. Specific humidity was independently and negatively associated with influenza activity. Combinations of low temperature (<18°C) and low specific humidity (<11 g/kg) were significantly associated with increased influenza activity.ConclusionsOur study broadens understanding of the relationships between seasonal influenza activity and meteorological factors in the Kenyan context. While rainfall is frequently thought to be associated with influenza circulation in the tropics, the present findings suggest low humidity is more important in Kenya. If annual vaccination were a component of a vaccination strategy in Kenya, the months of April to June are proposed as optimal for associated campaigns.
Highlights
Influenza exerts a significant health burden on human populations across temperate, sub-tropical and tropical regions.[1, 2] In temperate regions, influenza epidemics exhibit clear seasonality with peaks during winter months[3, 4] suggestive of an association with climatic factors
The proportion of patients who tested positive for influenza ranged from 4% in Kilifi to 19% among patients who were seen at Dadaab refugee camp
The median age of the patients who were tested for influenza was 1.7 years [interquartile range (IQR)=0.8-4.2 years] (Table 1)
Summary
Influenza exerts a significant health burden on human populations across temperate, sub-tropical and tropical regions.[1, 2] In temperate regions, influenza epidemics exhibit clear seasonality with peaks during winter months[3, 4] suggestive of an association with climatic factors. In these regions lower temperature, and lower specific humidity have been shown to be significantly associated with increased influenza activity.[5, 6] In contrast, influenza seasonal characteristics are less predictable in tropical and sub-tropical regions which are characterized by semi-annual epidemics or year-round influenza activity. Information on the timing of influenza circulation remains scarce in Tropical regions of Africa
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