Abstract
This study aimed to determine the role of influenza-like illness (ILI) surveillance conducted on Leyte Island, the Philippines, including involvement of other respiratory viruses, from 2010 to 2013. ILI surveillance was conducted from January 2010 to March 2013 with 3 sentinel sites located in Tacloban city, Palo and Tanauan of Leyte Island. ILI was defined as fever ≥38°C or feverish feeling and either cough or running nose in a patient of any age. Influenza virus and other 5 respiratory viruses were searched. A total of 5,550 ILI cases visited the 3 sites and specimens were collected from 2,031 (36.6%) cases. Among the cases sampled, 1,637 (75.6%) were children aged <5 years. 874 (43.0%) cases were positive for at least one of the respiratory viruses tested. Influenza virus and respiratory syncytial virus (RSV) were predominantly detected (both were 25.7%) followed by human rhinovirus (HRV) (17.5%). The age distributions were significantly different between those who were positive for influenza, HRV, and RSV. ILI cases were reported throughout the year and influenza virus was co-detected with those viruses on approximately half of the weeks of study period (RSV in 60.5% and HRV 47.4%). In terms of clinical manifestations, only the rates of headache and sore throat were significantly higher in influenza positive cases than cases positive to other viruses. In conclusion, syndromic ILI surveillance in this area is difficult to detect the start of influenza epidemic without laboratory confirmation which requires huge resources. Age was an important factor that affected positive rates of influenza and other respiratory viruses. Involvement of older age children may be useful to detect influenza more effectively.
Highlights
Influenza is an acute viral respiratory infection that affects 5%–15% of the global population and leads to approximately 250,000–500,000 deaths annually worldwide [1]
The percentage of cases sampled to total Influenza-like illness (ILI) cases was highest in 2013 and the differences between the years were significant (p < 0.001)
The fact that the proportion of older children and adults were smaller than young children in the proportion of ILI count might partly reflect unwilling to come to the hospital
Summary
Influenza is an acute viral respiratory infection that affects 5%–15% of the global population and leads to approximately 250,000–500,000 deaths annually worldwide [1]. Because of the public health significance, many countries have established their own influenza surveillance programs. Influenza surveillance is conducted for different objectives, including monitoring of circulating viruses, antiviral drug susceptibility, trends and impact of seasonal epidemics, and emergence of viruses with a pandemic potential. This surveillance provides useful information to both public health authorities and medical professionals. Previous studies have revealed that the detection rates of influenza range from 8.2% to 36.6% [6,7,8,9,10]
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