Let the sun shine in: effects of ultraviolet radiation on invasive pneumococcal disease risk in Philadelphia, Pennsylvania

Abstract

BackgroundStreptococcus pneumoniae is a common cause of community acquired pneumonia and bacteremia. Excess wintertime mortality related to pneumonia has been noted for over a century, but the seasonality of invasive pneumococcal disease (IPD) has been described relatively recently and is poorly understood. Improved understanding of environmental influence on disease seasonality has taken on new urgency due to global climate change.MethodsWe evaluated 602 cases of IPD reported in Philadelphia County, Pennsylvania, from 2002 to 2007. Poisson regression models incorporating seasonal smoothers were used to identify associations between weekly weather patterns and case counts. Associations between acute (day-to-day) environmental fluctuations and IPD occurrence were evaluated using a case-crossover approach. Effect modification across age and sex strata was explored, and meta-regression models were created using stratum-specific estimates for effect.ResultsIPD incidence was greatest in the wintertime, and spectral decomposition revealed a peak at 51.0 weeks, consistent with annual periodicity. After adjustment for seasonality, yearly increases in reporting, and temperature, weekly incidence was found to be associated with clear-sky UV index (IRR per unit increase in index: 0.70 [95% CI 0.54-0.91]). The effect of UV index was highest among young strata and decreased with age. At shorter time scales, only an association with increases in ambient sulphur oxides was linked to disease risk (OR for highest tertile of exposure 0.75, 95% CI 0.60 to 0.93).ConclusionWe confirmed the wintertime predominance of IPD in a major urban center. The major predictor of IPD in Philadelphia is extended periods of low UV radiation, which may explain observed wintertime seasonality. The mechanism of action of diminished light exposure on disease occurrence may be due to direct effects on pathogen survival or host immune function via altered 1,25-(OH)2-vitamin-D metabolism. These findings may suggest less diminution in future IPD risk with climate change than would be expected if wintertime seasonality was driven by temperature.

Sunshine, rainfall, humidity and child pneumonia in the tropics: time-series analyses

“…Increased ambient UV radiation could act to reduce pathogen survival in the environment, as has been suggested previously 16 . Time spent indoors may be reduced on sunny days in our study setting, potentially limiting crowding and exposure to indoor smoke, both known risk factors for lower respiratory infections 23 .…”

“…Increased relative humidity was associated with increased IPD incidence in New Zealand, but not in Australia 12, 13 . Low sunlight and temperature are consistently associated with high pneumonia incidence in time series studies in temperate settings, where annual peaks of lower respiratory infections occur during the short days of winter 10,[12][13][14][15][16] . The association between temperature and respiratory infections in children is inconsistent in time series studies from tropical settings, suggesting temperature is unlikely to be an important driver of pneumonia incidence in the tropics [6][7][8][9][10][11] .…”

“…Respiratory syncytial virus (RSV) infections were positively correlated with the number of rainy days and relative humidity in Indonesia and Malaysia, positively correlated with relative humidity and dew point in Mexico, and positively correlated with relative humidity in Hong Kong, although in Singapore a negative correlation with relative humidity was found [6][7][8][9][10][11] . In temperate settings where pneumonia peaks in winter, time series analyses have consistently found peaks of RSV and invasive pneumococcal disease (IPD) to be inversely correlated with temperature and daylight hours 10,[12][13][14][15][16] . Although daylight hours vary less in tropical latitudes, sunshine hours can vary seasonally according to cloud cover (and hence are generally lowest in the rainy season).…”

Antimicrobial implications of vitamin D

“…The virulence of the pathogen and the efficacy of host immune function boosted by 1,25-D 3 may determine the outcomes of invasive disease. 100 A doubleblind individually randomized placebo-controlled trial involving young children in an inner-city hospital in Kabul showed that the risk of a repeat episode of pneumonia within 90 days of supplementation of oral 100,000 IU of vitamin D 3 was lower in the intervention than in the placebo group. 101 Bahr et al examined group A streptococcal infections and found a striking association between vitamin D-binding protein (Gc2) and rheumatic fever in a homogeneous Arab population.…”

Pneumonia: A Challenging Health Concern with the Climate Change

“…Possible explanations of the seasonality seem to be the closer contact as a result of indoor crowding, lower humidity, induced variations in the human immune responses, indoor air pollution, low exposition to sunlight and ultraviolet (UV) radiation, keeping in mind the bactericidal effect of the latter [16]. In tropical regions, climate change also affects the pattern and seasonability of infections.…”