Case identification
Children aged 0–14 years were followed via annual surveys in addition to clinic visits where care givers were asked to bring their children at the first sign of illness. In this study, our primary outcome is symptomatic real-time reverse-transcription polymerase chain reaction (RT-PCR)-positive hMPV cases of children brought to clinic. Samples were tested using real-time reverse-transcription polymerase chain reaction (RT-PCR) if children met specific clinical features: 1) Reported fever (37.8C) or feverishness with cough, sore throat or runny nose for children aged 2 years and older, 2) Only fever or feverishness for children under 2, 3) Severe respiratory symptoms as evaluated by a physician including wheezing, chest indrawing, apnea etc., and 4) Hospitalization with respiratory symptoms or sepsis.
Our secondary outcome was hMPV-associated Acute Lower Respiratory Infection (ALRI), which was determined as patients that presented with a diagnosis of bronchiolitis, bronchitis, bronchopneumonia, or pneumonia or bronchial hyper-reactivity as determined by study physicians. To assess hMPV-associated ALRI, we selected all clinic visits that met the ALRI criteria occurring up to fourteen days prior to the clinic visit or 28 days after an hMPV-positive RT-PCR. HMPV positive tests spaced more than 30 days apart with different symptom onset dates were considered separate episodes. If the hMPV positive tests were less than 30 days apart, the first symptom onset date was used.