Children with asthma tend to have worse symptoms at the same times each year: when school starts in the fall and after school holidays in the spring.
Researchers previously thought that environmental factors such as air quality in schools might be to blame, but a new study confirms that the primary driver of seasonal waves of worsening asthma symptoms, which can lead to hospitalizations, is the common cold.
“The school calendar predicts common cold transmission, and the common cold predicts asthma exacerbations.”
“This work can improve public health strategies to keep asthmatic children healthy. For example, at the riskiest times of year, doctors could encourage patient adherence to preventative medications, and schools could take measures to reduce cold transmission,” says Lauren Meyers, professor of integrative biology and statistics and data sciences at the University of Texas at Austin.
Exacerbations, the medical term for worsening asthma symptoms, result in millions of missed work and school days and $50 billion in direct health care costs in the United States each year, researchers say.
Earlier studies into the cause of exacerbations involved swabbing individual patients to detect viruses, but Meyers, a mathematical biologist, and her team investigated population-wide patterns of how common colds circulate among adults and children throughout the year to learn about the role of the viruses.
The researchers built a computer model that incorporated possible drivers of asthma exacerbations and compared the output of the model to a large set of real-world health data: the timing and locations of about 66,000 asthma hospitalizations from cities across Texas during a seven-year period. By testing each driver independently, the researchers could determine the relative impact of each and find the weighted combination of factors that best fit the data.
The findings, published in the Proceedings of the National Academy of Sciences, show that the spread of cold viruses, which is heavily influenced by the school calendar, is the primary driver of asthma exacerbations.
“The school calendar predicts common cold transmission, and the common cold predicts asthma exacerbations,” says Meyers. “And this study provides a quantitative relationship between those things.”
The authors speculate on the mechanism behind this relationship: When children are out of school, they tend to spend less time with other children and are exposed to fewer viruses. As a result, their viral immunity decreases. When they return to school, they are exposed to viruses at much higher rates, and this is also the time when they are most susceptible.
The researchers also found that for adults, unlike children, the primary driver of asthma exacerbations is prevalence of the flu virus.
The study also developed more accurate rates of transmission of cold viruses than have been produced by previous studies—information that might help shed light on how common colds spread, and how we can protect people who are most vulnerable to them.
Researchers from Yale University and from the London School of Hygiene & Tropical Medicine are coauthors of the study.
The National Institute of General Medical Sciences funded the work.
Source: University of Texas at Austin