SAN FRANCISCO After investigating a meningococcal outbreak in the West, the Centers for Disease Control and Prevention (CDC) concluded that maternal smoking may be a major risk factor for disease transmission, according to Bradley A. Perkins, MD.
"The most remarkable finding was that childhood exposure to maternal smoke was associated with a fourfold rise in risk of disease," said Perkins, chief of the special pathogens section, Childhood and Respiratory Diseases Branch at the CDC. Perkins spoke here at the recent meeting of the American College of Physicians.
In 1994, Oregon reported 143 cases of meningococcal disease, an overall disease rate of five cases per 100,000 people, which is five times the national average. In addition, two counties in Washington reported 34 cases in a population of 380,000, which is about nine times the national average. This high incidence rate prompted an epidemiologic and laboratory investigation; both state health departments collaborated with the CDC in the investigation.
The population-based study enrolled patients with invasive disease from Oregon and Washington and compared them with control populations. "We had remarkable findings from this study that we think would be helpful in controlling disease to a certain extent," Perkins said.
They looked at independent risk factors in children younger than 18 years old and found a number of socioeconomic factors that put people at risk for disease: not having a primary care physician; crowding in the home; having a mother with little education; and smoking.
"Because this was a population-based study," Perkins said, "we were able to calculate the fraction of disease that could be attributed to different risk factors. We found that 40% of disease in children younger than 18 years of age were associated with maternal smoking. Because of the media attention that meningococcal disease gets, we think this may be a strong public health message and aid to the anti-smoking campaign."
In addition, the investigators looked at risk factors in adults and found that predisposing immunosuppressive illnesses, such as cancer, were a risk factor for disease, but so was smoking. "We also found that smoking in adults, both passive smoke exposure or active smoking, was a strong risk factor for disease," Perkins said. The association was so strong, in fact, that it accounted for one-third to one-half of the disease in that population.
The investigators surmised that smoking within the family increases the risk of disease because Neisseria meningitidis needs to colonize the nasal mucus of the throat prior to invasion, and either smoking products directly disrupt the mucosal surface or the smoke "paralyzes" the active phagocytes. Either mechanism would accentuate the colonizing of the throat and allow the organism to pass more easily from one person to another, according to Perkins.
"An additional hypothesis is that smokers and those around smokers are more likely to develop viral infections, which have been shown in some studies to be important co-factors for invasive meningococcal disease," he explained.
"Stopping people from smoking is a challenge," Perkins said. "Even if we did [convince everyone to stop smoking], we are not going to eliminate all the meningococcal disease, so we are concerned about having a vaccine that is appropriate for outbreak control."
Although there is no current vaccine available that is immunogenic against the serogroup B strain of N. meningitidis implicated in this and many other outbreaks, there are three being studied in several countries outside of the United States. These vaccines appear to be efficacious in early testing. "We hope to have this [a U.S.] vaccine for use under special circumstances within the next couple of years," Perkins said.
In the meantime, physicians have one more argument to persuade their patients to quit smoking.
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