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Background: Influenza virus is the most common cause of influenza-like illness (ILI) in adults. In Argentina, studies on influenza and other respiratory viruses were performed mostly in pediatric populations.
Objectives: To determine: (1) the frequency of influenza virus and other common respiratory viruses in adult outpatients with ILI, (2) whether the signs and symptoms predict viral etiology, (3) whether viral diagnosis changes clinical management or infection control measures and (4) to characterize the influenza strains circulating in the community.
Population and Methods: Nasal and pharyngeal swabs from adult outpatients with ILI attending the emergency room during the winter seasons of 2004 and 2005 in Argentina were evaluated by immunofluorescence and RT-PCR.
Results: Of 151 samples analyzed, 39 (26%) were influenza A positive, 5 (3·3%) influenza B positive and 4 (2·6%) respiratory syncytial virus positive by immunofluorescence. Two samples (1·3%) were human metapneumovirus positive by RT PCR. Cell culture detected six additional influenza viruses and one adenovirus positive sample. The sensitivity of immunofluorescence for influenza compared with culture was 70%. Symptoms did not predict etiology.
Conclusions: In this study, 40% of the patients with ILI had a specific viral infection and 83% were influenza viruses. Viral detection was necessary to determine the etiology as signs and symptoms were not different between patients with or without viral infection. Viral diagnosis was important to implement infectious control measures. Circulating influenza strains in this study were similar to the correspondent vaccine strains selected for the Southern hemisphere.
Viral respiratory infections are the most common acute illness worldwide. Influenza (Flu) virus is the most frequent cause of influenza-like illness (ILI) in adults. They usually present as abrupt, self-limited febrile infections that occur in outbreaks almost every winter. The attack rates during such periods have been reported to be as high as 10–40%. Other viruses implicated are respiratory syncycial virus (RSV), adenovirus, parainfluenza, rhinovirus and in a lower frequency, coronavirus and enterovirus. New viruses such as human metapneumovirus (hMPV), bocavirus, the new coronaviruses (NL 63) and polyomavirus (KI, WU) have been recently identified. Limited information is available about their significance and frequency in non-hospitalized adult patients although they can also cause severe respiratory illness.
All age groups are affected by Flu infection but serious complications occur more frequently in young children, immunocompromised patients and the elderly. These infections can lead to inadequate antibiotic use, numerous outpatient visits, and increased mortality in elderly nursing home patients. Several studies have reported that other viruses such as RSV and even bacteria can cause similar signs and symptoms. Therefore, rapid viral diagnosis is important to install antiviral treatment and to detect Flu outbreaks.
Surveillance studies have been done mainly in developed countries, and data from Argentina come mainly from pediatric populations.
The purpose of this study was to determine the frequency of influenza virus in young adult outpatients with ILI and to compare with the frequency of the other common respiratory viruses (RSV, adenovirus, parainfluenza viruses as well as hMPV). In addition, we evaluated whether the signs and symptoms predicted viral etiology and whether the use of indirect immunofluorescence (IIF) changed the clinical management and infection control measures. Flu strains recovered from this study were compared with those recommended for the annual Flu vaccine.
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