Effect of antipyretics on performance of influenza surveillance in Ghana

The World Health Organization's case definition for influenza-like illness (ILI) includes a measured temperature of ≥38°C. We conducted this study to assess the effect of antipyretics on performance of ILI surveillance in Ghana.

A cross-sectional study was conducted in two districts of Ghana from September 2013 to May 2014. We collected epidemiological data and respiratory specimens from an expanded ILI case definition, which included patients presenting to health facilities with measured temperature ≥38°C or reported fever (but afebrile at the time of evaluation), and cough, with onset in the last 10 days. Specimens were tested for influenza viruses by real time reverse-transcription polymerase chain reaction.

Of 321 participants who met our expanded ILI case definition, 236 presented with temperature of <38°C but reported subjective fever. Of these, 17% (39/236) were positive for influenza virus; Of those with fever ≤38°C who took antipyretics, 21%(16/77) were positive for influenza, compared with 14%(23/159) of those who did not take antipyretics. The addition of subjective fever to the standard ILI case definition captured approximately an additional 57% influenza cases but also required testing of approximately four times as many patients. However, including those without fever on presentation that had taken antipyretics found an additional 23% of Influenza cases and only two times as much testing.

Depending on the goals of surveillance (monitoring virus circulation or determining disease burden) and available resources, a more sensitive case definition including subjective fever and history of use of antipyretics may be warranted.