Oseltamivir ring prophylaxis for containment of 2009 H1N1 influenza outbreaks.
BACKGROUND
From June 22 through June 25, 2009, four outbreaks of infection with the pandemic influenza A (H1N1) virus occurred in Singapore military camps. We report the efficacy of ring chemoprophylaxis (geographically targeted containment by means of prophylaxis) with oseltamivir to control outbreaks of 2009 H1N1 influenza in semiclosed environments.


METHODS
All personnel with suspected infection were tested and clinically isolated if infection was confirmed. In addition, we administered postexposure ring chemoprophylaxis with oseltamivir and segregated the affected military units to contain the spread of the virus. All personnel were screened three times weekly both for virologic infection, by means of nasopharyngeal swabs and reverse-transcriptase-polymerase-chain-reaction assay with sequencing, and for clinical symptoms, by means of questionnaires.


RESULTS
A total of 1175 personnel were at risk across the four sites, with 1100 receiving oseltamivir prophylaxis. A total of 75 personnel (6.4%) were infected before the intervention, and 7 (0.6%) after the intervention. There was a significant reduction in the overall reproductive number (the number of new cases attributable to the index case), from 1.91 (95% credible interval, 1.50 to 2.36) before the intervention to 0.11 (95% credible interval, 0.05 to 0.20) after the intervention. Three of the four outbreaks showed a significant reduction in the rate of infection after the intervention. Molecular analysis revealed that all four outbreaks were derived from the New York lineage of the 2009 H1N1 virus and that cases within each outbreak were due to transmission rather than unrelated episodes of infection. Of the 816 personnel treated with oseltamivir who were surveyed, 63 (7.7%) reported mild, nonrespiratory side effects of the drug, with no severe adverse events.


CONCLUSIONS
Oseltamivir ring chemoprophylaxis, together with prompt identification and isolation of infected personnel, was effective in reducing the impact of outbreaks of 2009 H1N1 influenza in semiclosed settings.
Lee
Vernon J
VJ
Biodefence Centre, Ministry of Defence, Department of Epidemiology and Public Health, National University of Singapore. vernonljm@hotmail.com
Yap
Jonathan
J
Cook
Alex R
AR
Chen
Mark I
MI
Tay
Joshua K
JK
Tan
Boon Huan
BH
Loh
Jin Phang
JP
Chew
Seok Wei
SW
Koh
Wee Hong
WH
Lin
Raymond
R
Cui
Lin
L
Lee
Charlie W H
CW
Sung
Wing-Kin
WK
Wong
Christopher W
CW
Hibberd
Martin L
ML
Kang
Wee Lee
WL
Seet
Benjamin
B
Tambyah
Paul A
PA
D000293:Adolescent; D000998:Antiviral Agents / Q000009:adverse effects / Q000627:therapeutic use*; D015373:Bacterial Typing Techniques; D003140:Communicable Disease Control / Q000379:methods; D004196:Disease Outbreaks / Q000517:prevention & control*; D018562:Disease Transmission, Infectious / Q000517:prevention & control; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000235:genetics; D007251:Influenza, Human / Q000188:drug therapy / Q000453:epidemiology* / Q000517:prevention & control / Q000635:transmission; D008297:Male; D008889:Military Personnel; D053139:Oseltamivir / Q000009:adverse effects / Q000627:therapeutic use*; D010802:Phylogeny; D012846:Singapore / Q000453:epidemiology; D055815:Young Adult
D000998:Antiviral Agents; D053139:Oseltamivir