TABLE 2

Correlation analyses exploring the association within and between environmental factors and detection of influenza types and subtypesa

VariablePearson’s correlation coefficient
AHRHTempWSTemp fluctuation
RH0.08
Temp0.91−0.03
WS−0.38−0.10−0.38
Temp fluctuation0.150.010.19−0.19
Influenza A virus−0.330.24−0.280.26−0.06
Influenza A/H3N2 virus−0.350.26−0.40.19−0.08
Influenza B virus−0.26−0.20−0.450.260.11
All influenza viruses−0.270.07−0.310.19−0.01
  • a AH, absolute humidity; RH, relative humidity; WS, wind speed. Weekly medians were used to measure AH, RH, temperature, WS, and temperature fluctuation. Pearson’s correlation coefficients range from −1 to 1, with negative values indicating a negative association and positive values indicating a positive association. The strength of the association is interpreted as weak when coefficients are in the range of 0.1 to 0.3, medium when the coefficients are in the range of 0.4 to 0.7, and strong when the coefficients are in the range of 0.7 to 1.0. Temperature fluctuation was calculated as the median daily temperature of the assumed exposure date minus the median temperature on the previous day. The weekly median of temperature fluctuation was used for this analysis. Influenza A and B viruses represent the weekly total counts of influenza A and B virus-positive specimens. Influenza A virus represents the sum of the weekly counts of both influenza A and B viruses. Analyses for influenza A/H3N2 virus were restricted to influenza A virus-positive specimens that had subtyping performed.