3 Results
3.1 HMPV epidemiology
From April 2018 to March 2019, there were 900 males and 672 females
among the 1572 samples (sex ratio: 1.34:1), and the age range was from 1
day to 14 years of age with a median age of 3 years. The detection rate
of HMPV was 7.9% (124/1572), of which 78 were male and 46 were female,
with no significant gender difference (p =0.185). As shown in
Table 1, HMPV was detected among hospitalized children (< 14
years) with ARTIs at Beijing Friendship Hospital between April 2018 and
March 2019, and 78.2% (97/124) of children under 5 years old. The
seasonal distribution of HMPV cases in hospitalized children from April
2018 to March 2019 is shown in Figure. 1, and HMPV was detected
throughout the year. 34.7%(43/124)cases of HMPV infection were
detected in spring, 13.4%(17/124)in summer, 13.4%(17/124)in autumn
and 37.9%(47/124)in winter, and there were significant differences in
HMPV detection rates in different seasons (p = 0.000). From
September 2020 to August 2021, A total of 232 hospitalized children with
ARTIs were enrolled in this study, among which 134 (57.8%) were male
and 98(42.2%) were female (sex ratio: 1.34:1). The detection rate of
HMPV was 1.7% (4/232), which was significantly lower than that of the
previous year, and the 3 positive cases were children under 5 years old.
3.2 Detection of viral co‑infection in HMPV‑positive
specimens
A total of 124 HMPV-positive samples were detected during the period
from April 2018–March 2019, of which 62.9% (78/124) of HMPV
single-infected samples and 37.1% (46/124) of HMPV co-infected samples
with other respiratory viruses. Among the 46 co-infected cases, there
were 32 males and 14 females (sex ratio:2.29:1), with no statistical
significance for gender (p = 0.238). As shown in Table 2, the
most common mixed infection virus was HPIV3 (32.6%,15/46), and the
mixed infection rates with HRV, ADV, FLV-A, and RSV were 19.6% (9/46),
17.4% (8/46), 17.4% (8/46), and 10.9% (5/46), respectively. The viral
load of the 124 HMPV positive cases ranged from 14 copies/mL to
4.6×106 copies/mL NPA, with no statistical difference
in viral load between HMPV mono-infection and coinfection. From
September 2020 to August 2021, among the NPAs samples from 232
hospitalized children with ARTIs, 4 were HMPV-infected, with viral loads
ranging from 19 copies/mL to 3.16×103 copies/mL NPA. 2
cases were combined with other respiratory virus infections, which were
mixed with HBOV and HRV respectively.
3.3 Clinical characteristics of HMPV
infections
From April 2018 to March 2019, among the 124 children with HMPV
infection, 115 (92.7%) were diagnosed with pneumonia, 8 (6.5%) with
bronchitis, and 1 with upper respiratory tract infection (0.8%). The
main clinical symptoms of children with HMPV infection were cough
(95.2%, 118/124) and fever (91.9%, 114/124), and other symptoms
included rhinorrhoea (53.2%, 66/124), nasal obstruction (29.8%,
37/124) 124), sneeze (15.3%, 19/124) and Shiver (8.1%, 10/124). There
was no statistical difference in the above clinical symptoms between
children with HMPV single infection and mixed infection, as shown in
Table 3. The hospitalization time of HMPV-infected children was 2-14
days, and the average hospitalization time was 6.35 days. A total of 90
children were discharged within 7 days (72.6%, 90/124). Statistics on
the number of children who were hospitalized for more than 7 days showed
no significant difference between HMPV combined with other viral
infections and HMPV single infection (p =0.320).
3.4 HMPV genotyping and phylogenetic
analysis
Nested PCR was used to amplify the conserved sequence (610bp) of the F
gene in 128 HMPV-positive samples, and the target fragment was amplified
from 78 (63.0%, 78/124) HMPV-positive samples from April 2018 to March
2019. Phylogenetic analysis showed that 64 strains (82.1%, 64/78)
belonged to A2b subtype, 9 strains (11.5%, 9/78) B1 subtype and 5
strains (6.4%, 5/78) B2 subtype, A1 and A2a subtype was not found in
Figure2. As shown in Figure3, the viral load of A2b subtype samples was
significantly higher than that of B type samples (p =0.009), and
there was a statistically significant difference in the hospitalization
time >7 days between the two subtypes (p =0.031).
From September 2020 to August 2021, among the 4 HMPV-infected children,
only 1 case was positive for F gene amplification, and was identified as
B1 subtype by phylogenetic analysis.