Timely accessibility to healthcare resources and heatwave-related mortality in 7 major cities of South Korea: a two-stage approach with principal component analysis.

Background: Due to the ongoing effects of climate change, the incidence of heatwave-related mortality is rising globally. Improved allocation and utilization of healthcare resources could help alleviate this issue. This study aimed to identify healthcare resource factors associated with heatwave-related mortality in seven major cities of South Korea. Methods: We analyzed daily time-series data on mean temperature and all-cause mortality from 2011 to 2019. Using principal component analysis (PCA), we clustered district-level healthcare resource indicators into three principal components (PCs). To estimate district-specific heatwave-mortality risk, we used a distributed lag model with a quasi-Poisson distribution. Furthermore, a meta-regression was performed to examine the association between healthcare resources and heatwave-mortality risk. Findings: A total of 310,363 deaths were analyzed in 74 districts. The lag-cumulative heatwave-related mortality (RRs) ranged from 1.12 (95% confidence interval [CI]: 1.07, 1.17) to 1.21 (95% CI 1.05, 1.38), depending on the definitions used for heatwaves. Of the three PCs for healthcare resources (PC1: pre-hospital emergency medical service, PC2: hospital resources, PC3: timely access), timely access was associated with reduced risk of heatwave-related mortality, particularly among the elderly. Specifically, timely access to any emergency room (ER) exhibited the strongest association with lower heatwave-related mortality. Interpretation: Our findings suggest that timely access to any ER is more effective in reducing heatwave-related mortality risk than access to higher-level healthcare facilities, especially among the elderly. Therefore, healthcare resource factors and ER accessibility should be prioritized when identifying vulnerable populations for heatwaves, along with known individual and socio-demographic factors. Funding: This work was supported by the Research Program funded by the Korea Disease Control and Prevention Agency (2022-12-303), the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (No. 2022R1A2C2092353) and the MD-PhD/Medical Scientist Training Program through the Korea Health Industry Development Institute (KHIDI), funded by the Ministry of Health & Welfare, Republic of Korea.

Disparities in the association between ambient temperature and preterm birth according to individual and regional characteristics: a nationwide time-stratified case-crossover study.

BACKGROUND: Several studies have reported that climate change elevates heat exposure in pregnant women and high temperatures during pregnancy are associated with preterm births (PTBs). Although the association might be disproportionate, related evidence remains sparse. We evaluated the disproportionate risk of PTB associated with ambient temperature during pregnancy by individual and regional characteristics in South Korea. METHODS: We collected data on birth certificates and daily mean temperatures during the period from 2011 to 2019. A time-stratified case-crossover design was used to investigate the association between temperature and PTB and stratified analyses were conducted to examine the effect modification of individual and regional characteristics. RESULTS: A total of 160,067 singleton PTBs were recorded in Korea from 2011 to 2019. A 5℃ increase in the mean temperature during the last four weeks before delivery was associated with an increased risk of PTB with an odds ratio (OR) of 1.03 (95% confidence interval [CI]: 1.02, 1.05), and the association was more evident in mothers aged ≥35 years (OR: 1.06 [95% CI: 1.03, 1.10]) and with low education levels (OR: 1.04 [95% CI: 1.02, 1.05]). Additionally, the estimated risk was evident in districts with lower medical resources and more prominent disparities were shown by individual and regional characteristics in rural areas than in urban areas. CONCLUSIONS: This study provides evidence that the risk of PTB related to ambient temperature is disproportionate by individual and regional characteristics and suggests the need for public health policies to alleviate the disparities, especially in rural areas.

Fluctuating risk of acute kidney injury-related mortality for four weeks after exposure to air pollution: A multi-country time-series study in 6 countries.

BACKGROUND: Recent studies have reported that air pollution is related to kidney diseases. However, the global evidence on the risk of death from acute kidney injury (AKI) owing to air pollution is limited. Therefore, we investigated the association between short-term exposure to air pollution-particulate matter ≤ 2.5 µm (PM2.5), ozone (O3), and nitrogen dioxide (NO2)-and AKI-related mortality using a multi-country dataset. METHODS: This study included 41,379 AKI-related deaths in 136 locations in six countries during 1987-2018. A novel case time-series design was applied to each air pollutant during 0-28 lag days to estimate the association between air pollution and AKI-related deaths. Moreover, we calculated AKI deaths attributable to non-compliance with the World Health Organization (WHO) air quality guidelines. RESULTS: The relative risks (95% confidence interval) of AKI-related deaths are 1.052 (1.003, 1.103), 1.022 (0.994, 1.050), and 1.022 (0.982, 1.063) for 5, 10, and 10 µg/m3 increase in lag 0-28 days of PM2.5, warm-season O3, and NO2, respectively. The lag-distributed association showed that the risk appeared immediately on the day of exposure to air pollution, gradually decreased, and then increased again reaching the peak approximately 20 days after exposure to PM2.5 and O3. We also found that 1.9%, 6.3%, and 5.2% of AKI deaths were attributed to PM2.5, warm-season O3, and NO2 concentrations above the WHO guidelines. CONCLUSIONS: This study provides evidence that public health policies to reduce air pollution may alleviate the burden of death from AKI and suggests the need to investigate the several pathways between air pollution and AKI death.

Heat wave exposure and increased heat-related hospitalizations in young children in South Korea: A time-series study.

BACKGROUND: Numerous studies have investigated the association between heat wave exposure increased heat-related hospitalizations in the general population. However, little is known about heat-related morbidity in young children who are more vulnerable than the general population. Therefore, we aimed to evaluate the association between hospitalization for heat-related illness in children and heat wave exposure in South Korea. METHODS: We used the National Health Insurance Service (NHIS) database, which provides medical records from 2015 to 2019 in South Korea. We defined daily hospitalizations for heat-related illness of children younger than five years during the summer period (June to August). We considered the definition of heat waves considering the absolute temperature and percentile. A total of 12 different heat waves were used. A time-series analysis was used to investigate the association between heat wave exposure and heat-related hospitalization among children younger than five years. We used a two-stage design involving a meta-analysis after modeling by each region. RESULTS: We included 16,879 daily heat-related hospitalizations among children younger than five years. Overall, heat wave exposure within two days was most related for heat-related hospitalizations in young children. The relative risk (RR) due to heat wave exposure within two days (lag2) (12 definitions: 70th to 90th percentile of maximum temperature) ranged from 1.038 (95% confidence interval (CI): 0.971, 1.110) to 1.083 (95% CI: 1.036, 1.133). We found that boys were more vulnerable to heat exposure than girls. In addition, we found that urban areas were more vulnerable to heat exposure than rural areas. CONCLUSIONS: In our study, heat wave exposure during summer was found to be associated with an increased risk of hospitalization for heat-related illness among children younger than five years. Our findings suggest the need for summer heat wave management and prevention for children.

Effect of PM concentration on anemia blood indicators reduced by air purifiers.

Housewives perform daily household chores, which directly expose them to indoor particulate matter (PM). Indoor PM exposure is a potential factor that increases systemic inflammation and affects hematopoietic action. This study investigated the decrease in indoor PM concentration by air purifiers on indicators of anemia, such as hemoglobin, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC). We analyzed the data of 40 housewives who were subjected to an air purifier intervention in Seoul and Ulsan, Republic of Korea. Indoor exposure levels of PM2.5 and PM10 were analyzed with sensor adjusted and gravimetric measurement. We also investigated the same anemia indicators before and after the installation of an air purifier for three months (short-term: one month, long-term: three months). Statistical analysis was performed by a multiple linear model and a linear mixed model. The indoor PM exposure levels and air purifier use were related to anemia indicators (hemoglobin and MCHC). The increase in indoor PM2.5 level was associated with a decrease in MCHC (ß: 0.034, P = 0.031) and hemoglobin (ß: 0.013, P = 0.04). The decrease in indoor PM2.5 concentration by air purifier was associated with an increase in MCHC (ß: 0.204, P = 0.087) and hemoglobin (ß: 0.190, P = 0.039). In particular, after air purifier intervention, the amounts of MCHC and hemoglobin significantly increased. Our results suggest that indoor air purifier use could decrease indoor PM level and the risk of anemia to housewives. Because the effect on anemia is subacute, it was confirmed three months after air purifier operation. In conclusion, anemia indicators can be improved by PM reduction management.

Direct and Indirect Effects of Indoor Particulate Matter on Blood Indicators Related to Anemia.

Exposure to indoor particulate matter (PM) is a potential risk factor that increases systemic inflammation and affects erythropoiesis. This study investigated the association between exposure to indoor PM and blood indicators related to anemia (BIRA) in housewives. Indoor PM and blood folate status are important factors in the risk of anemia. This was a housewife cohort study; we recruited 284 housewives in Seoul and Ulsan, Republic of Korea. Indoor exposure to PM2.5 and PM10 was measured by gravimetric analysis and sensors. We investigated the BIRA, such as hemoglobin (Hb), hematocrit, mean corpuscular volume (MCV), mean corpuscular Hb (MCH), and mean corpuscular Hb concentration (MCHC). Statistical analysis was performed by multiple linear regression model and mediation analysis. The association between BIRA and PM was assessed by multiple linear regression models fitted by mediation analyses. The increase in the level of indoor PM2.5 was associated with a decrease in MCV (Beta coefficient (B): -0.069, Standard error (SE): 0.022) and MCH (B: -0.019, SE: 0.009) in gravimetric measurements. The increase in the level of indoor PM2.5 was associated with a decrease in Hb (B: -0.024, SE: 0.011), hematocrit (B: -0.059, SE: 0.033), and MCV (B: -0.081, SE: 0.037) and MCH (B: -0.037, SE: 0.012) in sensor measurements (PM2.5-Lag10). Further, we identified a serum folate-mediated PM effect. The indoor PM exposure was significantly associated with decreased Hb, MCV, and MCH in housewives. Taken together, our data show that exposure to indoor PM is a risk factor for anemia in housewives. Blood folate concentration can be a mediating factor in the effect of indoor PM on BIRA. Therefore, folate intake should be recommended to prevent anemia in housewives. Moreover, indoor PM exposure should be managed.

Indoor particulate matter and blood heavy metals in housewives: A repeated measured study.

BACKGROUND: Particulate matter (PM) less than 2.5 µm in diameter and 10 µm (PM10) contains heavy metals, but whether exposure to PM is significantly associated with the burden of heavy metal exposure in the population is unknown. We investigated the association between exposure to PM and blood concentrations of lead (Pb), cadmium (Cd), and mercury (Hg) in Korean housewives. MATERIALS & METHODS: From July 2017 to January 2020, we recruited 115 housewives in Ulsan, Republic of Korea. After excluding participants with missing information, we finally included 88 Korean housewives in our study. We measured the concentrations of indoor PM using a gravimetric method 24 h before blood sampling and the concentrations of Cd, Pb, and Hg in blood, twice at a 1-year interval. We used a linear mixed effect model to estimate the associations between indoor PM and blood heavy metals. RESULTS: Exposure to PM10 was significantly associated with blood concentrations of Cd among Korean housewives. A 10 µg/m3 increase of PM10 the previous day was associated with a 2.8% (95% confidence interval (CI) = 1.1%, 4.6%) and a 1.5% (95% CI = -0.1%, 3.1%) increase in blood concentrations of Cd and Pb in the linear mixed effect model, respectively. CONCLUSION: There was a significant association between indoor PM exposure and blood Cd concentrations among Korean housewives. This result suggests that the body burden of heavy metals is significantly associated with air pollution.

The Combined Effects of Fine Particulate Matter and Temperature on Preterm Birth in Seoul, 2010-2016.

Background: Preterm birth contributes to the morbidity and mortality of newborns and infants. Recent studies have shown that maternal exposure to particulate matter and extreme temperatures results in immune dysfunction, which can induce preterm birth. This study aimed to evaluate the association between fine particulate matter (PM2.5) exposure, temperature, and preterm birth in Seoul, Republic of Korea. Methods: We used 2010-2016 birth data from Seoul, obtained from the Korea National Statistical Office Microdata. PM2.5 concentration data from Seoul were generated through the Community Multiscale Air Quality (CMAQ) model. Seoul temperature data were collected from the Korea Meteorological Administration (KMA). The exposure period of PM2.5 and temperature were divided into the first (TR1), second (TR2), and third (TR3) trimesters of pregnancy. The mean PM2.5 concentration was used in units of ×10 µg/m3 and the mean temperature was divided into four categories based on quartiles. Logistic regression analyses were performed to evaluate the association between PM2.5 exposure and preterm birth, as well as the combined effects of PM2.5 exposure and temperature on preterm birth. Result: In a model that includes three trimesters of PM2.5 and temperature data as exposures, which assumes an interaction between PM2.5 and temperature in each trimester, the risk of preterm birth was positively associated with TR1 PM2.5 exposure among pregnant women exposed to relatively low mean temperatures (<3.4 °C) during TR1 (OR 1.134, 95% CI 1.061-1.213, p < 0.001). Conclusions: When we assumed the interaction between PM2.5 exposure and temperature exposure, PM2.5 exposure during TR1 increased the risk of preterm birth among pregnant women exposed to low temperatures during TR1. Pregnant women should be aware of the risk associated with combined exposure to particulate matter and low temperatures during TR1 to prevent preterm birth.

Effect of heat waves and fine particulate matter on preterm births in Korea from 2010 to 2016.

BACKGROUND: Previous studies have reported that fine particulate matter (PM2.5) affects the incidence of premature births. In addition, recent studies have suggested that heat waves have a negative impact on birth outcomes. However, the combined effect of PM2.5 and heat waves on the incidence of premature birth is controversial. This study investigated the independent and combined effects of PM2.5 and heat wave exposures during the 1st and 2nd trimesters on premature birth. METHODS: The National Statistical Office of Korea provided birth data from 2010 to 2016. Preterm birth was defined as birth between 22 and 36 weeks. To assess the exposure to PM2.5 and heat waves, we used PM2.5 data estimated by the Community Multiscale Air Quality Modeling System (CMAQ) and heat wave warning data provided by the Korea Meteorological Administration. A multivariate logistic regression was used to investigate the risk of preterm birth according to the exposure to PM2.5 and heat waves during the 1st and 2nd trimesters, and it was adjusted for residential area, year of birth, season of birth, parity, education level of the mother, age of the mother, and sex of the baby. RESULTS: In the 2nd trimester, compared with the 0 h of heat wave exposure (≤67 percentile), 62.50-314.00 h (79-88 percentile) and>315.00 h of heat wave exposure (>88 percentile) were both significantly associated with preterm birth (OR for 79-88 percentile, 1.037, 95% CI, 1.003-1.073; OR for > 88 percentile, 1.174, 95% CI, 1.134-1.215). However, PM2.5 exposure was not significantly associated with preterm birth. On the other hand, in the analysis to evaluate the combined effect of PM2.5 and heat wave exposures of the 2nd trimester, compared with 0 h of heat wave exposure (≤67 percentile) and<11.64 µg/m3 (≤25 percentile) of PM2.5, 11.64-22.74 µg/m3 (≤25 percentile), 22.74-27.58 µg/m3 (26-50 percentile), and 27.57-32.39 µg/m3 (51-75 percentile) of PM2.5 exposure combined with>315.00 h of heat wave exposure (>88 percentile) were all significantly associated with preterm birth. In addition, the effect size was increased with an increase of PM2.5 exposure (OR for ≤ 25 percentile, 1.148, 95% CI, 1.095-1.203; OR for 26-50 percentile, 1.248, 95% CI, 1.178-1.323; OR for 51-75 percentile, 1.370, 95% CI, 1.245-1.507). CONCLUSION: Our findings suggest that the combined effect of heat wave and PM2.5 exposure during the 2nd trimester on the risk of preterm birth was greater than that of each exposure alone. In other words, exposure to PM2.5 increases the impact of heat waves on the risk of preterm birth. These results indicate that control of prenatal exposure to fine particular matter and extreme temperatures is important for the prevention of preterm birth.

The impact of PM2.5 on acute otitis media in children (aged 0-3): A time series study.

BACKGROUND: Experimental studies have reported that air pollution could make the middle ear more susceptible to infections. However, the associations between specific air pollutants and AOM were inconsistent in previous epidemiologic studies. This study aimed to investigate the association between PM2.5 exposure and the AOM events in seven major cities in the Republic of Korea. METHODS: We performed a nationwide time series analysis of children aged 0-3 years living in seven major Korean cities between 2008 and 2016. We used a quasi-Poisson regression to estimate the short-term association between incident AOM and the 5-day moving average of particulate matter smaller than 2.5 µm (PM2.5) for each city. Then, we conducted a meta-analysis to combine the city-specific associations. The exposure unit was 10 µg/m3, and all models were adjusted for time, daily mean apparent temperature and day of the week. RESULTS: A higher risk of incident AOM was significantly associated with higher 5-day moving PM2.5 averages in five cities, except for Gwangju and Ulsan. The combined relative risk (RR) was 1.011 (95% confidence interval [CI]: 1.008, 1.014). In the subgroup analysis by season, PM2.5 exposure was significantly associated with incident AOM in the warm season (RR: 1.016, 95% CI: 1.009, 1.022). In addition, among children with a URI history within 4 weeks, children with a more recent URI history were more sensitive to the impact of PM2.5 exposure on incident AOM (RR for 1st week: 1.017, 95% CI: 1.011, 1.024; RR for 2nd week: 1.013, 95% CI: 1.008, 1.018; RR for 3rd week: 1.008, 95% CI: 1.003, 1.013; RR for 4th week: 1.005, 95% CI: 1.001, 1.009). CONCLUSION: Higher PM2.5 concentrations are associated with a higher risk of incident AOM, particularly in the warm season and children with recent URI history. Our findings could have important implications for preventing AOM in children.