Influenza excess mortality from 1950-2000 in tropical Singapore.
BACKGROUND
Tropical regions have been shown to exhibit different influenza seasonal patterns compared to their temperate counterparts. However, there is little information about the burden of annual tropical influenza epidemics across time, and the relationship between tropical influenza epidemics compared with other regions.


METHODS
Data on monthly national mortality and population was obtained from 1947 to 2003 in Singapore. To determine excess mortality for each month, we used a moving average analysis for each month from 1950 to 2000. From 1972, influenza viral surveillance data was available. Before 1972, information was obtained from serial annual government reports, peer-reviewed journal articles and press articles.


RESULTS
The influenza pandemics of 1957 and 1968 resulted in substantial mortality. In addition, there were 20 other time points with significant excess mortality. Of the 12 periods with significant excess mortality post-1972, only one point (1988) did not correspond to a recorded influenza activity. For the 8 periods with significant excess mortality periods before 1972 excluding the pandemic years, 2 years (1951 and 1953) had newspaper reports of increased pneumonia deaths. Excess mortality could be observed in almost all periods with recorded influenza outbreaks but did not always exceed the 95% confidence limits of the baseline mortality rate.


CONCLUSIONS
Influenza epidemics were the likely cause of most excess mortality periods in post-war tropical Singapore, although not every epidemic resulted in high mortality. It is therefore important to have good influenza surveillance systems in place to detect influenza activity.
Lee
Vernon J
VJ
Biodefence Center, Ministry of Defence, Singapore, Singapore. vernonljm@hotmail.com
Yap
Jonathan
J
Ong
Jimmy B S
JB
Chan
Kwai-Peng
KP
Lin
Raymond T P
RT
Chan
Siew Pang
SP
Goh
Kee Tai
KT
Leo
Yee-Sin
YS
Chen
Mark I-Cheng
MI
D004196:Disease Outbreaks; D006801:Humans; D007251:Influenza, Human / Q000401:mortality* / Q000821:virology; D009975:Orthomyxoviridae / Q000302:isolation & purification; D012846:Singapore / Q000453:epidemiology; D014329:Tropical Climate