Prevalence & Seasonal Incidence
HCoV-NL63 was first isolated from a 7-month-old baby with bronchiolitis in early 2004;[13] at approximately the same time, essentially the same virus (named HCoV-NL) was isolated from an 8-month-old boy suffering from pneumonia.[16] The virus has since been detected in 1.0–9.3% of respiratory tract samples collected in different countries indicating a global distribution (Table 1).[5,17–33]
In a study testing the serum samples of 139 children, HCoV-NL63 seroconversion occurred before the age of 3.5 years, with 75% of children in the age group 2.5–3.5 years found to be seropositive.[34] In another report, the seroprevalence of HCoV-NL63 in 6–12-month-old children was 28.6–40.0%.[35] Maternally acquired antibodies were present in newborns and usually decreased within the first 4–5 months of life.[34,35] Three studies have calculated the incidence of HCoV-NL63 infections.[5,19,36] The design of these studies varied, however, and differences in the calculated incidences were reported. The comprehensive study by van der Hoek and colleagues[5] calculated the overall annual incidence in outpatients as seven per 1000 children per year, with the hospitalization rate estimated at 22 per 100,000 children; in contrast, a hospitalization rate of 224 per 100,000 (children younger than 6 years old) as previously reported.[19]
At present, the accuracy of HCoV detection is hampered by three difficulties. First, the suitability of the clinical samples examined: a recent study has demonstrated that there are differences between respiratory samples collected by nose/throat swabs, and those collected by nasopharyngeal aspiration, specifically regarding their usefulness in detecting and identifying respiratory pathogens.[37] The second problem is that diagnostic tests for HCoVs are not frequently used in the routine testing for respiratory viruses, which probably results in the percentage of HCoVs infections being greatly underestimated.[38] Lastly, over the years several molecular methods of variable sensitivity were used to determine the incidence of the virus.[39–41] Unless sensitive and specific nucleic acid amplification tests are used for the detection of CoVs (including those infections with low viral load) as part of a respiratory virus surveillance strategy, the CoVs will always be underdiagnosed.[42]
Even though the majority of initial reports identified winter as the peak season for HCoV-NL63 infections, other studies reported seasonal variations for HCoV-NL63 infections, including spring and autumn for China,[19] and summer for Taiwan.[43] Also, although a study from Thailand, with its tropical climate, showed year-to-year variation in prevalence of HCoV-NL63 infections, the virus was detected throughout the year.[44] A recent comprehensive 2-year population-based study, using data from different countries, on children under 3 years of age with lower respiratory tract infection (LRTI) shows that HCoV-NL63 infections peak in winter months. This study also shows large year-to-year differences in the frequency of HCoV-NL63 infections, with results indicating an interepidemic period of 2 years.[5]
Future Microbiol. 2011;6(2):153-159. © 2011 Future Medicine Ltd.
Cite this: Human Coronavirus NL63 - Medscape - Feb 01, 2011.
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