RSV Infection Is Seasonal, Age-Dependent, According to 10-Year Study in China

Respiratory syncytial virus (RSV) epidemics appeared to last from October to March with a peak in summer in southwest China, according to a study published in the Journal of Medical Virology. The researchers also found that infants who were born 1 to 2 months before the start of RSV season were more susceptible to infection.

Acute lower respiratory tract infection (ALRTI) is a primary cause of mortality in children 5 years and younger. Previous studies found that RSV accounted for 18.7% of cases of acute respiratory infections in China, with infants having the highest prevalence (26.5%) and most children being younger than 1 year when infected. This current study aimed to determine the seasonality of RSV and its association with infections in infants.

Children aged 1 month to 5 years who had an LRTI and were admitted to the respiratory ward were recruited from June 2009 to May 2019. All participants were tested for RSV, parainfluenza virus (PIV), influenza virus, metapneumovirus, human coronavirus, human rhinovirus (HRV), human bocavirus, and human adenovirus. Cases with a discharge diagnosis of bronchitis, bronchiolitis, or pneumonia were defined as LRTI cases.

Hospital information systems were used to collect data on demographics, chief complaint, and primary diagnosis, medical history, and laboratory tests. All participants also had nasopharyngeal aspirates that were collected. Seasonality analyses were done using the average annual percentage (AAP) method, which arranged the RSV positive cases in each week from high to low and considered the epidemic weeks those that made up the top 75% of cases, and the percent positivity method, in which RSV positivity rates were calculated by calendar month and year.

The study enrolled 6991 cases, of which 34.5% were positive cases for RSV. The annual rates of positive RSV cases ranged from 28.4% to 39.0%, with all but 2012/2013 having a rate higher than 30%.

The epidemic year was defined as the year that started from week 25 in June to week 24 of the following May. The epidemic season for RSV was narrowed down to week 43 in October to week 13 in March of the following year to last 24 weeks, according to the AAP method. The percent positivity method found similar results, with the average epidemic lasting for 9 months from August to the next April when calculating the positive rate of RSV on a monthly basis with a threshold of 20%. The epidemic lasted for 6 months from October to March of the next year when the threshold of 30% was used.

A total of 4354 infants 1 year and younger with LRTI were included in the analysis, with an overall positive rate of 39.3%. The positive rate of RSV in infants born in May and August through December was more than 40%. The researchers found that infants were more likely to be infected with RSV when they were younger, with those born in May and August through December more likely to be infected with RSV than other infants.

A potential limitation of this study is that it was conducted in only 1 hospital in southwest China. The study population also solely included inpatients with LRTI who were aged 1 month to 5 years. Data from after the COVID-19 pandemic were also not included.

The researchers concluded that the RSV epidemic season extended from October to March and that infants who were born in May and August through December, or 1 to 2 months before the start of the RSV season, were more susceptible to being infected with RSV themselves.

Reference

Li T, Fant H, Liu X, et al. Defining RSV epidemic season in southwest China and assessing the relationship between birth month and RSV infection: a 10-year retrospective study from June 2009 to May 2019. J Med Virol. 2023;95:e28928. doi:10.1002/jmv.28928