Epidemiological isolation causing variable mortality in Island populations during the 1918-1920 influenza pandemic.
BACKGROUND
During the 1918 pandemic period, influenza-related mortality increased worldwide; however, mortality rates varied widely across locations and demographic subgroups. Islands are isolated epidemiological situations that may elucidate why influenza pandemic mortality rates were so variable in apparently similar populations.


OBJECTIVE
Our objectives were to determine and compare the patterns of pandemic influenza mortality on islands.


METHODS
We reviewed historical records of mortality associated with the 1918-1920 influenza pandemic in various military and civilian groups on islands.


CONCLUSIONS
Mortality differed more than 50-fold during pandemic-related epidemics on Pacific islands [range: 0.4% (Hawaii) to 22% (Samoa)], and on some islands, mortality sharply varied among demographic subgroups of island residents such as Saipan: Chamorros [12%] and Caroline Islanders [0.4%]. Among soldiers from island populations who had completed initial military training, influenza-related mortality rates were generally low, for example, Puerto Rico (0.7%) and French Polynesia (0.13%). The findings suggest that among island residents, those who had been exposed to multiple, antigenically diverse respiratory pathogens prior to infection with the 1918 pandemic strain (e.g., less isolated) experienced lower mortality. The continuous circulation of antigenically diverse influenza viruses and other respiratory infectious agents makes widespread high mortality during future influenza pandemics unlikely.
Australian Army Malaria Institute, Enoggera, Qld, Australia. dennis.shanks@defence.gov.au
G Dennis
GD
Shanks
Tracy
T
Hussell
John F
JF
Brundage
D049673:History, 20th Century; D006801:Humans; D007251:Influenza, Human / Q000453:epidemiology* / Q000266:history / Q000401:mortality*; D008889:Military Personnel; D010139:Pacific Islands / Q000453:epidemiology; D058873:Pandemics / Q000266:history*; D016019:Survival Analysis