Burden and epidemiology of respiratory viruses in Hong Kong

Abstract

Respiratory viral infections (RVIs) cause a substantial burden of morbidity and mortality among children worldwide, particularly in children age under five years of age. However, vaccination, as the optimal means of disease prevention, is currently not available for most respiratory viruses. Apart from influenza virus (IFV) and respiratory syncytial virus (RSV), the epidemiology and disease burden of many RVIs have not been comprehensively studied.

I investigated the etiology, seasonality and other epidemiology features of respiratory viral infections in Hong Kong children based on a series of datasets from ill children in the general community, from outpatient clinics, and from hospitals. I also used population-based mortality and morbidity data. I fitted statistical models to the data to characterize the seasonality and examine the correlation of seasonal patterns with climactic factors. I used regression models to estimate excess hospitalizations and mortality. I assessed the severity by comparing statistical estimates of the impact of each disease at different levels of the pyramid of disease.

I found that entero/rhinoviruses, influenza viruses and coronaviruses were more frequently detected among all children regardless of symptoms, with human metapneumovirus also more commonly detected in symptomatic children and parainfluenza virus among those asymptomatic children. The overall duration of symptoms of those with positive detection of a respiratory virus was about 8.2 days. Clinical characteristics of these respiratory viruses were similar except for significant difference in fever, cough and mean age. Younger children (aged 0-5 years) had a higher frequency of virus detection and a longer symptomatic duration than the older children (aged 6-15 years). All non-influenza viruses together(RSV: 182, CI: 95-269; PIV,122, CI:34-209; AdV, 120, CI: 43-201) were associated with an estimated 423 excess respiratory hospitalizations per 100,000 person-years, similar to those caused by influenza viruses (422, CI: 341-501) in children. Common respiratory viruses were associated with 0.21 to 4.35 excess respiratory intensive care unit (ICU) admissions per 100,000 person-years, with 3.54 for influenza virus and 9.11 for all non-influenza viruses together. None of the viruses were associated with significant excess mortality except for influenza A (H1N1) (0.11 per 100,000 person-years).

Both influenza and non-influenza respiratory virus infections were associated with substantial diseases burden in Hong Kong children. IFV and RSV contributed to the highest excess hospitalization and ICU admission rate. The risk of hospital to ICU admission was generally higher for non-influenza virus infections than IFV infections.

In conclusion, the impact and severity of respiratory viruses was greater in younger children compared to older children. Significant disease burden caused by non-influenza viruses underscores the importance of control of respiratory virus infections in children beyond influenza vaccination.