Seasonality and Seasonal Decomposition Analysis of hMPV
HMPV epidemics alternated years (Fig. 4). Years with the highest hMPV
incidence were 2011, 2013, and 2015. Cases tended to peak during
July–August, however there was additional variation of incidence
throughout the year, which was particularly notable in 2015 (Fig. 4 and
Supplemental Fig. 2). In 2012 and 2014 there was no major epidemic.
There was a rise in case numbers in 2016 in September–January which
differs from peaks in previous years, however it is possible that the
peak epidemic period occurred later into 2017 (Fig. 4, Supplemental Fig.
2).
When the trend (Tt ) was isolated from the
seasonal and remainder components in Classical Additive Decomposition,
there was no overall observable increase or decrease in the number of
monthly symptomatic hMPV cases (Fig. 5B). When the seasonality and
remainder were extracted from the trend there was a distinct decrease of
the number of cases in 2012 and 2014 (Fig. 5B), and an increase in cases
in 2013 and 2015. This trend was also noted in the remainder component
where there were significant increases and decreases that were not
explained by the trend (Tt ) or seasonal component
(St ) (Fig. 5C, D). The increases in symptomatic
hMPV cases when annual seasonal patterns (St ) and
longitudinal trend were extracted (Tt ) revealed a
biennial residual pattern.