CMV is a latent virus in the herpes family. Infection is common but the majority of people aren't symptomatic because the immune system keeps the virus under control. People of lower income and education lose immune control more easily, Dowd said. Their weakened immune systems, which may be due to increased levels of stress, make them more susceptible to other infections as well. "What is going on with the dramatic (downturn) in the economy could actually translate into people's susceptibility to these diseases," Dowd said.

CMV is thought to be a prime culprit in breaking down the immune system as we age, and CMV is also associated with chronic conditions like heart disease. In the study, a person with less than a high school education had the same level of immune control as someone 15-20 years older with more than a high school education, Dowd said.

"When you listen to the current news about H1N1, it's interesting because everyone feels that this is a random threat, that we all have an equal chance of getting it," Dowd said. "This study points out that certain groups are potentially more susceptible and it's not just people with existing chronic illness."

The study, "Socioeconomic Differentials in Immune Response," will appear in an upcoming issue of the journal Epidemiology.

Source: University of Michigan