April 13, 2010 -- Military personnel and young people had higher swine flu infection rates when the disease swept Singapore in 2009, a new study finds.
The finding comes from an analysis of blood samples taken from nearly 3,000 people before, during, and after the H1N1 swine flu was detected in Singapore from June to September 2009.
Scientists found variations in antibody levels in the groups tested, which included 838 people from the general population, 1,213 military members, 558 from an acute care hospital, and 300 people (staff and residents) from long-term care facilities.
In blood samples drawn before or early in the epidemic, high levels of titers were found in 2.6% of the general population, 9.4% of military personnel, 6.6% of hospital staff, and 6.7% of people at long-term care facilities. Titer is a term used to describe the concentration of antibodies in the blood.
Researchers looked for a fourfold increase in antibody titers over time in the second or third blood sample to indicate that a person had developed a new case of swine flu infection during the epidemic time period. The researchers say 13% of people in the community participating in the study developed a new swine flu infection during the epidemic, a finding that “supports the case for targeted vaccination in populations.”
“Our study also shows the variation in infection risks, with younger age groups and military personnel having much higher infection rates,” the authors write. “The lower infection rates in older participants corroborate other epidemiological observations.”
The study also shows that people “with higher baseline titers have significantly lower infection rates, perhaps indicative of protection against 2009 A (H1N1) infection.”
The researchers say the wide variations in antibody development in various age groups suggest that interventions need to be tailored to the population at risk.
The study is published in the April 14 issue of the Journal of the American Medical Association.