Wildfire Air Pollution Linked With Increased Rates of Psoriasis Clinic Visits Among Adults

Air pollution from wildfires is associated with increased rates of clinic visits for psoriasis over time among adult patients, according to findings of a research letter published recently in JAMA Network Open.

The link between air pollutants and risk of flare and more severe disease in patients with psoriasis has been demonstrated previously, albeit with limited evidence. The air pollutant particulate matter (PM) is of notable importance regarding risk, as previously reported data indicate that exposures to coarse PM and fine PM in the 60 days before assessment were associated with a higher risk of worsening disease in patients with psoriasis.

Similar adverse effects of PM exposure have been shown among patients with other inflammatory conditions such as asthma, atopic dermatitis, and chronic rhinosinusitis with nasal polyps.

“Wildfires are increasing in many parts of the world, which may contribute to worsening air pollution in some areas. During California wildfires in 2018 and 2020, clinic visits and online search interest in atopic dermatitis and itch increased, but online search interest in psoriasis did not,” said the study authors. “On a molecular level, air pollutants cause upregulation of several genes associated with inflammation and psoriasis, which could be associated with disease flare.”

They sought to investigate whether clinic visits and online search interest in psoriasis were associated with wildfire air pollution after a delayed lag period. A cross-sectional analysis was conducted to characterize air pollution in San Francisco using 3 key metrics:

• Fire status (binary indicator of whether a wildfire occurred during a week)
• Concentration of PM 2.5 mcm or less in diameter (_PM2.5) measured at ground level
• Smoke plume density (range, 0-3, where 0 indicates none, 1 indicates light, 2 indicates medium, and 3 indicates heavy) based on satellite imaging
  

Data were collected for outpatient dermatology visits for psoriasis at an academic medical center in San Francisco from October 1, 2018, to February 10, 2019 (including the California Camp Fire); October 1, 2015, to February 10, 2016 (no fires); and October 1, 2016, to February 10, 2017 (no fires). Statistical analysis was performed from December 20, 2021, to March 10, 2022.

“The California Camp Fire occurred 175 miles away from San Francisco and was associated with worsened air quality in San Francisco from November 8 to 21, 2018,” they explained.

Outcome data on psoriasis clinic visits were stratified by age group (< 18 and > 18 years) and analyzed using generalized Poisson regression. Statistical models included 11 one-week exposure lags and were adjusted for temperature, humidity, age, year, and overall patient volume at clinics. Weekly online search interest data (​​eg, search value index [SVI]) were additionally collected from Google Trends for the term psoriasis in San Francisco in 2018.

A total of 986 clinic visits for 471 patients with psoriasis (mean [SD] age, 46.7 [19.1] years; 248 male patients [52.7%]; 106 Asian patients[22.5%]; 12 Black patients [2.5%]; and 289 White [61.1%] patients) were assessed, of which 914 visits were for adults [> 18 years] and 72 visits for children [< 18 years])

In examining psoriasis clinic visits by fire status for adults, adjusted data from the 11 one-week exposure lags showed that the earliest statistically significant increase in adult visits occurred at the 5-week lag (risk ratio [RR], 1.32; 95% CI, 1.02-1.70) and peaked at the 8-week lag (RR, 1.45; 95% CI, 1.13-1.86) and 9-week lag (RR, 1.45; 95% CI, 1.12-1.87).

The mean weekly SVI for psoriasis from October 4, 2018, to January 30, 2019, showed an increase in search volume also starting 5 weeks after the fire and peaking at week 8. No statistically significant results were found for pediatric patients.

As these analyses focused on only 1 wildfire affecting a city distant from its origin, the researchers noted that findings likely underestimate the overall burden of skin disease associated with wildfires and communities experiencing greater smoke exposure.

The low number of participating children was also cited as a potential limitation of the findings, as well as the proportional underrepresention of minority racial and ethnic populations of San Francisco in the study.

“Future studies should include other locations with wildfires, which will likely affect the medical services of many health care systems,” concluded the researchers. “Understanding environmental triggers is important for appropriately counseling patients regarding the risk of pollution-induced psoriasis flares as wildfires increase.”

Reference

Fadadu RP, Green M, Grimes B, et al. Association of wildfire air pollution with clinic visits for psoriasis. JAMA Netw Open. 2023 Jan 3;6(1):e2251553. doi:10.1001/jamanetworkopen.2022.51553