2.2 Epidemiological characteristics of RSV infections
From March 2015 to February 2019,
we observed a yearly RSV epidemic
around Winter as expected. RSV detection rate began to rise in October,
peaked in December or the following January, and fell to an ordinary
level in April, with about 90% of RSV infections occurring during the
epidemic season (from October to the following March) (Fig. 1A, B). In
different years, the RSV epidemic season may advance or be delayed by
about one month. Two groups of RSV (RSV-A and RSV-B) were prevalent each
year, but RSV-A remained predominant from March 2015 to February
2019. The proportion of RSV-A
infection among total RSV-positive cases was 62.8%. (Fig. 1C)
RSV detection rate was the highest in the 0-year-old group (9.98%),
followed by the 1-year-old group (6.18%), and the 2–4-years-old group
(4.92%); it decreased significantly to a low level in 5–44 years group
(5–13 yr: 1.68%; 14–17 yr: 0.61%; 18–44 yr: 0.57%), and increased
in the 45–59 years of age adults (1.15%), and more obviously in the
elderly persons with 60 years of age or older (1.57%) (Fig. 2A). Both
RSV-A and RSV-B were detected in all age groups, with RSV-A a dominant
proportion (Fig. 2A). For further analysis, the above mentioned nine age
groups were incorporated into four age groups as 0–4 years (subtotal of
detection rate: 6.07%), 5–17 years (subtotal of detection rate:
1.51%), 18–59 years (subtotal of detection rate: 0.76%), and 60 years
or older (subtotal of detection rate: 1.57%).
The proportion of RSV infections
under five years old (52%) among the total RSV infections was the
greatest, followed by that of the elderly adults with 60 years of age or
older (25%); the top two groups accounted for 77% of RSV infections
(Fig. 2B).
The RSV detection rate of pneumonia cases (NSCAP and SCAP) was higher
than that of AURTI cases by age group, which showed that RSV was more
prone to cause acute lower respiratory tract infection. However, the RSV
detection rate of NSCAP cases was slightly higher than that of SCAP
cases despite no significant difference observed. Although RSV-A and
RSV-B were both detected among each class of RSV infection in each age
group, RSV-A approximately dominated in each
group (Fig. 3).
The most common co-existing pathogen identified from RSV-positive cases
was the influenza virus (10.2%), followed by M. pneumoniae(4.1%; Fig. 4).