Higher risk for tuberculosis diagnosis with wildfire smoke exposure
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Key takeaways:
- Patients exposed to wildfire smoke vs. non-wildfire pollution had higher odds for tuberculosis diagnosis.
- Over 6 months, each air pollution event related to wildfires was linked to 23% increased odds for TB.
Heightened odds for a tuberculosis diagnosis were related to exposure to ambient air pollution that contained wildfire smoke, according to results published in American Journal of Respiratory and Critical Care Medicine.
“Our findings add to a growing list of adverse health outcomes associated with wildfire smoke exposures,” Lauren R. Linde, MPH, MCP, current epidemiologist with the CDC National Center for Immunization and Respiratory Diseases and a surveillance epidemiologist with the California Department of Public Health at the time of the study, and colleagues wrote. “Although we estimated a modest increase in the risk of TB diagnosis with each wildfire smoke exposure in this study, the high prevalence of TB globally and the increasing frequency of wildfires may underscore considerable disease burden associated with such exposures.”
In a case-crossover study, Linde and colleagues evaluated 6,238 patients (70% 45 years or older; 60% male; 62% Asian/Pacific Islander) who received a TB diagnosis between 2014 and 2019 across eight counties in California to figure out if there is a link between these diagnoses and acute outdoor air pollution exposure, specifically related to wildfire smoke.
Researchers looked at each patient’s exposure to particulate matter less than 2.5 µm in diameter (PM2.5) daily with knowledge of their home address via geocoding. Linde and colleagues specifically evaluated patients’ pollution exposure within 6 months of receiving a diagnosis of TB, defined as the hazard period.
Days during which mean PM2.5 levels went above 35 µg/m3 were defined by researchers as PM2.5 events; these events became wildfire-associated events if the address was inside the area of a smoke plume.
Researchers assessed how often patients were exposed to wildfire and non-wildfire PM2.5 events to understand how each are related to TB risk.
In the 6-month timeframe prior to TB diagnosis, 3,139 patients were a part of at least one PM2.5 event. From this cohort of patients, 671 were a part of at least one wildfire-associated event, whereas 2,783 patients experienced non-wildfire events.
A higher percentage of PM2.5 events related to wildfires happened during the hazard period than non-wildfire events (35% vs. 24%). Additionally, when evaluating PM2.5 events that went over 100 µg/m3 in each group, researchers observed more wildfire related events compared with non-wildfire events (13% vs. < 1%).
With every increasing risk period up to 180 days, researchers found that each PM2.5 event meant higher adjusted odds for TB. At 90 days, each event meant 1% (95% CI, 0%-3%) higher odds for a TB diagnosis, and this went up to 5% (95% CI, 3%-6%) at 180 days.
Despite elevated odds seen with each PM2.5 event, these odds went up even higher when a patient was exposed to a wildfire associated PM2.5 event. At 90 days, each wildfire related event meant an 11% (95% CI, 7%-15%) increased odds for TB diagnosis, and this went up to 23% (95% CI, 19%-28%) at 180 days.
For non-wildfire associated pollution events, researchers found that these events are not linked to higher odds for a TB diagnosis.
“Although the case-crossover design provided an opportunity to assess the proximate effects of acute wildfire-associated PM2.5 exposures on TB diagnoses, prospective studies should characterize short-term and long-term effects of outdoor air pollution from various sources on differing aspects of TB infection risk and clinical course,” the researchers wrote.
This study by Linde and colleagues adds to growing literature about the harmful effects of PM2.5 air pollution, but further confirmation is necessary due to the latency period of TB, according to an accompanying editorial by William Checkley, MD, PhD, associate professor of medicine in the division of pulmonary and critical care at Johns Hopkins Medicine.
“As tuberculosis has an average latency of 3-9 months to 2 years, one would therefore assume that a 6-month exposure window used by Linde and colleagues was reasonable, but longer time exposure windows of up to 2 years may be warranted as sensitivity analyses,” Checkley wrote.
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Perspective
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I always say “Don’t light things on fire and breathe them into your lungs — this applies to tobacco, diesel, forests and more.” Tiny particulate matter (or PM2.5) is emitted from combustion. We know that people who inhale it through smoking cigarettes are at increased risk for tuberculosis infection. This study by Linde et al shows that when communities “smoke” in the setting of wildfire exposure, that can also increase the risk for active TB infection. In this case control study, there was an increased risk for diagnosis of active TB in the time period following wildfire events in which PM2.5 levels quickly increased into unhealthy and hazardous ranges.
The burden of climate change on our health is increasing every year. This is another aspect of the cost of climate change. Wildfires are becoming more frequent and more intense in the American West. I live in Oregon, and during wildfire events, we have had air that has been rated as “hazardous” or “beyond index” on the Air Quality Index.
It is not only increased TB transmission that we will see as our climate changes. PM2.5 and wildfire exposure have also been associated with increased risk for other infections. I host the Air Health Our Health podcast and interview a range of experts to educate clinicians, parents and the community at large on the health impacts of particulate matter, climate change, wildfires and more. I have featured episodes on the interaction between wildfires and the following flu season as well as on the deadly interaction of PM2.5 and COVID-19. PM2.5 alters the immune system in our lungs, and our changing climate and resulting wildfires will mean more PM2.5 in the air at a time when infectious diseases are also expanding their territories in a warming climate and with global travel.
So, what can doctors and health professionals do about this? First, we need to educate ourselves. I didn’t learn anything about particulate matter, wildfires and air pollution during my medical training. Part of the mission of Air Health Our Health is to ensure that we all know how climate change affects our health. Fortunately, if you can talk about cigarettes with your patients, you can talk about PM2.5.
This problem cannot be solved in our clinics and hospitals. We in health care also need to educate our communities. We need to advocate for ways to decrease the climate change that is driving these wildland fires and also for resiliency measures. For example, we need to ensure that there is access to clean indoor air in the time of wildfires, knowing how to talk about HEPA filters with our patients and how to avoid or mitigate other sources of indoor air pollution, such as gas stoves.
You can see a brief introduction on the interaction of climate change and particulate matter on health in this Healio video from Chest 2022. It is important for those in health care to learn how climate change and air pollution affect our health so we can work for cleaner air for all our patients.
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