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BACKGROUND: Human metapneumovirus (hMPV) was first identified approximately 13 years ago as an important cause of respiratory illness, especially among young children and older adults. However, it is infrequently included among routine diagnostic testing and surveillance. The Wisconsin Influenza Incidence Surveillance Project (WIISP) established routine surveillance in primary care clinics to monitor patients with acute respiratory illness (ARI) and test for multiple respiratory viruses.
METHODS: Data originated from four family medicine clinics in Dane County, Wisconsin from January 2011 through October 2014. Nasopharyngeal or posterior pharyngeal swabs were collected from all patients presenting within 7 days from onset and ≥2 of the following symptoms: rhinorrhea, nasal congestion, sore throat, cough, or fever. Demographic and clinical data were collected from each patient. Specimens were tested by the Wisconsin State Lab of Hygiene using a multiplex RT-PCR assay. Seasonal circulation of hMPV was determined as weeks during which the percent of specimens positive for hMPV was >1 standard deviation (S.D.) above the mean.
RESULTS: A total of 1945 patients with ARI presented to participating clinics during the surveillance period, of which 63 (3.2%) were RT-PCR positive for hMPV. In 2011 and 2013, 1.9 and 2.2% of ARI patients had an hMPV detection, respectively, each followed by years with significantly more frequent hMPV detection in 2012 and 2014 (4.1 and 4.8%, respectively p=.003). Circulation of hMPV was focused from January through April, encompassing 83% of total hMPV detections. The median season duration was 12 weeks, ranging from 19 weeks in 2012 to 5 weeks in 2013. Among all 63 hMPV positives, the median age was 35.4 years; however, detections were most common among children aged 0-5 years (n=16, 25.4%) and adults aged 25-50 years (n=21, 33.3%, p<0.05) compared with patients aged 5-17, 18-24, and >50 years. The most common symptoms associated with hMPV infection were cough (96.8%), nasal congestion (71.4%), rhinorrhea (69.8%), and fever (65.1%). Among children with an hMPV detection, 86% had a fever, compared with only 53% of adults (p=0.01).
CONCLUSIONS: The WIIISP provided year-round, age-specific hMPV surveillance among outpatients with ARI in Wisconsin. We demonstrated that hMPV is common among both children and adults, circulating most frequently between January and April with alternating seasonal intensity. The WIISP provided a successful platform to conduct enhanced epidemiologic characterization of this important respiratory pathogen within the ambulatory healthcare setting.