The bivariate correlation between three meteorological factors (total amount of rainfall, relative humidity and number of rain days) and number of influenza cases were significantly positive

The bivariate correlation between 3 meteorological factors (total sum of rainfall, relative humidity and number of rain days) and quantity of influenza circumstances have been drastically good (p < 0.05), while both particulate matter and ground temperature showed significant negative correlation (p < 0.05) with number of influenza cases (Table 1). Though, partial correlation showed that only ground temperature was significantly associated with the number of influenza cases (p < 0.05). A multiple linear regression analysis showed that the linear combination of all five meteorological factors (non-ordered predictors) was significantly related to the number of influenza cases (outcome) (R2 = 0.458, adjusted R2 = 0.329, F (5, 21) = 3.549, p < 0.05). Based on both linear correlational and regression analyses, ground temperature is perhaps the main predictor (standard regression coefficient, beta = -0.545, t (26) = -2.308, p < 0.05) which accounts for 40.5% (r: -0.636, R2 = 0.405) of the variance of the number of influenza cases, while the other variables contributed only an additional 5.3% (45.8%- 40.5% = 5.3%). However, such judgments about the relative importance of these predictors are challenging because they are also correlated among themselves (range of r: 0.407.931, p < 0.05, data not shown). Notable characteristic waves of influenza viruses were also observed (Fig 1C): First, influenza A cases consistently peaked ahead of influenza B and fell between September and January, whereas influenza B cases peaked later between February and April when influenza A cases decreased. Second, the overall prevalence of influenza B infection was consistently lower than that of influenza A virus.Fig 1. Seasonality of influenza infections and meteorological factors in Malaysia between 2012 and 2014. (A) Total UKI-1 rainfall Amount (mm), Mean Relative Humidity (%) and Number of Rain Days. (B) Mean Particulate Matter–PM10 (g/m3) and Ground Temperature (). (C) Monthly distribution of influenza A and B infections in Kuala Lumpur, Malaysia.A total of 168 full-length HA and 166 full-length NA gene sequences were obtained from 170 patients in the present study (S2 Table). Additional 23 Malaysian influenza B viruses with fulllength HA and NA gene sequences and collection dates from January 2012 to June 2014 were also retrieved from GISAID and GenBank databases. These published sequences were originated from the National Influenza Centre at the Institute of Medical Research (IMR) Malaysia. Hence, a total of 193 Malaysian influenza B viruses were included for phylogenetic classification. Phylogenetic analysis of the HA sequences (1,758bp) shows that 67.3% (113/168) of Malaysian influenza B viruses from this study belonged to22022974 Yamagata lineage, while 32.7% (55/168) viruses belonged to Victoria lineage (Fig 2, S1 Fig).