3.Discussion
Using hospital-based and multicenter surveillance for RSV infection among the all-age population in Beijing for four years, this study revealed the epidemiological characteristics of RSV in Beijing from 2015 to 2019: The RSV was prevalent in the all-age population in Beijing with only one annual epidemic season. Moreover, the RSV season started in October, ended in March of the following year with a single peak in Winter, and covered about 90% of RSV infections. The epidemic season’s onset and offset times in different years may advance or be delayed by about one month. However, the offset time of the RSV epidemic season we observed was not consistent with Yu et al.’s report[17]. The reason may be that they adopted the definition of the RSV epidemic season described previously by CDC in the U.S.[18], the consecutive weeks during which the RSV detection rate per week exceeds a threshold of 10%, which might be appropriate for RSV infections among children but not applicable in this study due to the inclusion of adults. Yu et al. also reported that RSV-A and RSV-B dominated alternatively in different years in Beijing from 2007 to 2015[17], but we observed that RSV-A has remained dominant in Beijing since 2015.
This study compared the prevalence of RSV infections among the populations of different age groups and found that the detection rate of RSV was highest in children under five years of age (6.07%), followed by people aged ≥60 years (1.57%). Ren et al[19] reported that the RSV detection rate in patients aged ≥66 years was 2% in Beijing during 2005–2007, the same percentage Feng et al.[10] reported for the average of RSV detection rates in patients aged ≥65 years from 22 provinces in China from 2009 to 2013. These two estimates are slightly higher than ours, probably due to the inclusion of the 60–64 years of age population in our study. However, our findings confirmed that the elderly people aged ≥60 years were another RSV infection susceptible population, accounting for 25.2% of total RSV infections, besides the expected children under five years of age, who accounted for 52.0%. Given that China is the world’s largest population country and its population is aging, it can be speculated that the proportion of RSV-infected patients with 60 years of age or older will increase continuously shortly. So, the elderly population, 60 years of age or older, should receive full consideration when the RSV prevention and control policy is made.
This study also found that co-infection of multiple pathogens was common in RSV-infected cases. The most frequently identified pathogens was the influenza virus, followed by M. pneumoniae , which might be due to a certain overlap of the epidemic seasons of RSV, influenza virus, andM. pneumoniae in Beijing[16].
Another contribution of this study was that we described and compared the clinical characteristics of patients with RSV infection from different age groups in Beijing, particularly patients 60 years or older. We found that the many key indicators of the patients with RSV infection among the elderly adult aged ≥60 years were significantly higher than those among the populations of any other age group, namely, the rate of hospitalization, the rate of ICU admission, and the rate of death in hospital. However, the RSV detection rate of the elderly adult aged ≥60 years was lower than that of children under five years old.
As to clinical manifestations, the most outstanding for RSV-infected patients with ≥60 years of age was dyspnea followed by lymphocytopenia, which was more common compared to other age groups, and occurred at a significantly higher frequency than the RSV-infected patients under five years of age. Regarding complications, there was an obvious difference in the different age groups. RSV infections in elderly adults aged ≥60 years were frequently complicated by respiratory failure, heart failure, and kidney failure compared to other populations, while acute myocardial injury was more common in RSV infections in children under five years of age. Notably, a total of eight RSV-infected patients with severe pneumonia were given ECMO therapy in this study, and finally, seven cases were cured, and one died. This favorable ratio suggests that there may be a chance to improve the hospitalization mortality of RSV-infected adults further and needs to be confirmed by collecting more cases.
Several studies reported the RSV infection in elderly adults focusing on different aspects, and considered that the RSV infection led to a heavier health burden and more severe illness in the elderly adults than influenza[2, 20, 21]. In this study, the hospital length of stay of patients with RSV infection was elevated as the age of the patients increased, the hospital length of stay in RSV-infected patients with ≥60 years was 12 days, and was longer than that of any other age group, but was shorter than the hospital stay of 20 days reported by Jin et al[20] for RSV-infected elderly adults in South Korea. The hospitalization mortality of RSV-infected patients aged ≥60 years is 7.8%, which was also significantly higher than that of children with RSV infection under five years of age (0%), and approximately consistent with the study of Falsey et al. [2] on American healthy elderly adults (mortality of 8% among RSV-infected patients aged ≥65 years), but lower than Jin’s[20] study on the elderly adults in South Korea (mortality of 12% among RSV-infected patients aged ≥65 years).
In conclusion, The RSV season in Beijing usually began in October and ended in March of the following year and covered approximately 90% of RSV infections. The RSV infection in the elderly aged ≥60 years old, the second most susceptible population, usually developed more severe outcomes than in children under five years of age, with dyspnea and lymphocytopenia as important clinical characteristics.These findings can promote the comprehensive understanding of the illness course and contribute to the policy-making on RSV prevention and control in China, particularly in Beijing.