A new study has untangled a complex web of factors behind high rates of asthma in the urban environment such as the connection between exposure to air pollution and asthma-related cockroach allergy. The children are hit from the outside with air pollution and from inside homes and schools with exposure to roaches.
An allergic reaction to cockroaches is a major contributor to asthma in urban children, but new research suggests that the insects are just one part of a more complex story. Very early exposure to certain components of air pollution can increase the risk of developing a cockroach allergy by age 7, and children with a common mutation in a gene called GSTM may be especially vulnerable. Air pollution primes kids for asthma-related cockroach allergy.
Researchers at the Columbia Center for Children’s Environmental Health at the Mailman School of Public Health published the findings, the first on this interplay of risk factors, in the February 6 online edition of the Journal of Allergy and Clinical Immunology.
“Allergy to cockroach is one of the greatest risk factors for asthma in low-income urban communities,” says lead author Matthew Perzanowski, PhD, in the February 6, 2013 news release, Air Pollution Primes Children for Asthma-Related Cockroach Allergy. “Our findings indicate a complex relationship between allergen and air pollution exposures early in life and a possible underlying genetic susceptibility. Combined, these findings suggest that exposures in the home environment as early as the prenatal period can lead to some children being at much greater risk for developing an allergy to cockroach, which, in turn, heightens their risk of developing asthma.”
Exposure to cockroach allergen before birth
Dr. Perzanowski and his co-investigators looked at 349 mother-child pairs from the Center’s Mothers & Newborns study of environmental exposures in Northern Manhattan and the Bronx. During the mother’s pregnancy, exposure to cockroach allergen (protein in feces, saliva, or other remnants of the insects) was measured by collecting dust from the kitchen and bed.
Researchers also sampled air to measure the mother’s exposure to polycyclic aromatic hydrocarbons, or PAH (combustion products that are harmful components of air pollution). Presence of the GSTM1 mutation was determined through blood samples. At ages 5 and 7, the children had blood tests to identify the presence of IgE antibodies—an immune marker of allergy.
Researchers tested participants for antibodies against cockroach allergen and looked at homes for remnants of roaches
The researchers found that 279 or 80% of homes tested positive for high levels of cockroach allergen. By age 7, 82 of 264 children tested, or 31%, had cockroach allergy. Presence of higher levels of cockroach allergen led to cockroach allergy only in children whose mothers also had been exposed to higher levels of PAH during pregnancy. This result, the authors say, suggests that PAH enhances the immune response to cockroach allergen.
The combined impact of the two exposures was even greater among the 27% of children with a common mutation in the GSTM gene. This mutation is suspected to alter the ability of the body to detoxify PAHs.
The studies suggests minimizing exposure to air pollution as well as roaches in the home and in school
The study suggests that minimizing exposure to PAH during pregnancy and to cockroach allergen during early childhood could be helpful in preventing cockroach allergies and asthma in urban children. “Asthma among many urban populations in the United States continues to rise,” says senior author Rachel Miller, MD, according to the news release. “Identifying these complex associations and acting upon them through better medical surveillance and more appropriate public policy may be very important in curtailing this alarming trend.”
Additional authors include Ginger L. Chew, Adnan Divjan, Kyung Hwa Jung, Robert Ridder, Deliang Tang, Diurka Diaz, Inge F. Goldstein, Patrick L. Kinney, Andrew G. Rundle, David E. Camann, and Frederica P. Perera.
The National Institute of Environmental Health Sciences (grant #s P01 ES09600, 5 RO1 ES08977, R01ES13163, RO1ES11158, P30 ES009089, P50ES015905, R03 ES013308), the U.S. Environmental Protection Agency (grant #s R827027, RD832141, RD834509), and private foundations supported this study.
Cockroach allergens in homes associated with prevalence of childhood asthma in some neighborhoods
Children living on NYC blocks where asthma is common have higher levels of exposure to cockroach allergens and are more likely to be sensitized to it. In New York City, the prevalence of asthma among children entering school varies by neighborhood anywhere from 3% to 19%, and children growing up within walking distance of each other can have 2-3 fold differences in risk for having asthma.
In the first comprehensive effort to understand what drives these localized differences, researchers at Columbia University's Mailman School of Public Health compared the household presence of cockroach, mouse, cat, dust mite and other allergens in neighborhoods with a high prevalence of asthma to that in low-prevalence neighborhoods. They found that cockroach, mouse and cat allergens were significantly higher in homes located in neighborhoods where asthma is more common and that children in these higher-exposure homes were more likely to be sensitized to cockroach antigens.
The full study is online in the Journal of Clinical Immunology. The researchers studied 239 children 7 to 8 years old who were recruited through the middle-income HIP Health Plan of New York, as part of the ongoing New York City Neighborhood Asthma and Allergy Study. A total of 120 children lived in high asthma prevalence neighborhoods and 119 were from low-prevalence areas. Based on a parent reported survey of symptoms, 128 were classified as having asthma and 111 were assigned to a control group.
Allergen exposure was measured by collecting and analyzing bed dust samples from the upper half of the children's beds
Sensitization was measured by screening blood samples for antibodies to various household allergens. Earlier studies of inner-city children have found that exposure and sensitization to cockroach and mouse allergens is associated with having asthma.
Researchers found that cockroach, mouse and cat allergens were more prevalent in the bed dust taken from homes in high asthma neighborhoods than low asthma neighborhoods, and that sensitivity to cockroach allergen was twice as common: 23.7% versus 10.8%. However, there was no significant difference by neighborhood in sensitization mouse and cat antigens.
"Our findings demonstrate the relevance of exposure and sensitization to cockroach, mouse, dust mite, and cat in an urban community and suggest that cockroach allergen exposure could contribute to the higher asthma prevalence observed in some New York City neighborhoods," said Matthew Perzanowski, PhD, associate professor of Environmental Health Sciences and senior author, according to the May 17, 2011 news release, "Cockroach allergens in homes associated with prevalence of childhood asthma in some neighborhoods."
"Although the relationships between allergen levels and household demographics have been examined in the U. S. on a national level, an advantage to focusing on a single city is the decreasing likelihood of confounding by regional differences, such as building types or climate," he explained in the news release. These findings combined point to cockroach allergen exposure potentially leading to a higher prevalence of asthma in some urban neighborhoods," said Dr. Perzanowski.
The neighborhood income was more important than the child's family income
Dr. Perzanowski also stresses that in this study of middle-income families in New York City it was a child's neighborhood income that was more important in predicting the likelihood of exposure to pests in the home than family income.
"In summary, significant differences in allergen exposure in homes throughout New York City have been demonstrated with this unique study cohort:
- cockroach allergen was higher in the homes of the high asthma prevalence neighborhoods,
- cockroach sensitization was higher among children living in neighborhoods with high rates of asthma,
- cockroach allergen exposure was associated with sensitization, and
- cockroach sensitization was associated with increased risk for asthma.