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Urinary Tract Infection

Hotter summer days brought more emergency admissions for urinary tract infection in Korea, and diabetes sharpened the effect

4,436 emergency visits across fourteen summers. A 20 percent rise in temperature carried an odds ratio of 1.06 overall — and 1.14 in people with diabetes.

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In short

In a national time-stratified case-crossover study using South Korean National Health Insurance Service data on 1,131,714 beneficiaries, covering all 4,436 emergency room admissions for urinary tract infection during the summers of 2006 to 2019 with satellite-derived daily temperatures assigned by each patient's residential district across 248 districts, a 20 percent increase in summer temperature over lag days 0 to 2 was associated with an odds ratio of 1.06 (95% CI 1.02 to 1.10) in the total population, rising to 1.11 (95% CI 1.05 to 1.17) in people aged 65 or over, 1.12 (95% CI 1.05 to 1.19) in women and 1.14 (95% CI 1.07 to 1.23) in people with a history of diabetes.

Key takeaways

  • 4,436 emergency room admissions for urinary tract infection were identified during the summers of 2006 to 2019 among 1,131,714 National Health Insurance Service beneficiaries.
  • A 20 percent increase in summer temperature over lag days 0 to 2 carried an odds ratio of 1.06 (95% CI 1.02 to 1.10) overall.
  • The association was stronger in people aged 65 or over (OR 1.11, 95% CI 1.05 to 1.17).
  • It was stronger in women (OR 1.12, 95% CI 1.05 to 1.19) and strongest in people with a history of diabetes (OR 1.14, 95% CI 1.07 to 1.23).
  • Exposure was satellite-derived daily average temperature for June to September, assigned by residential district across 248 districts.
  • The strength of the association increased across the study period in the total population.
  • A case-crossover design compares each patient with themselves on other days, so fixed personal characteristics cannot confound the result.

Urinary tract infection is not usually thought of as a seasonal illness, and the reason it turns out to be one is unglamorous: in heat people lose fluid through skin and lungs, urine concentrates, and the flushing that keeps bacteria out of the bladder happens less often.

Why the design removes most objections

A time-stratified case-crossover study compares each person who was admitted against the same person on control days in the same month. Age, sex, income, comorbidity, anatomy, hygiene and every other fixed characteristic are identical on both sides of the comparison, because both sides are the same individual. Nothing stable about a person can explain the result.

OR 1.14

odds of an emergency admission for urinary tract infection per 20 percent rise in summer temperature, among Koreans with a history of diabetesPark J et al., BMC Public Health, 2024

Who the heat reaches first

The overall effect is modest — an odds ratio of 1.06 is a 6 percent relative increase — and the subgroups are where it becomes a clinical statement rather than a climatological one. People over 65 came in at 1.11, women at 1.12 and people with diabetes at 1.14.

Each of those has a mechanism that fits. Thirst perception declines with age, so older people dehydrate further before they drink. Women have a shorter urethra and a higher baseline rate of infection for the heat to act on. Diabetes contributes from both directions at once: glucose in the urine feeds bacteria, and osmotic diuresis adds to the fluid loss that heat is already causing.

The trend inside the trend

The association strengthened over the fourteen years of the study in the total population. The authors do not resolve why, and there are at least two candidates that this design cannot separate: summers grew hotter, and the population grew older. Either would produce the same drift.

Two limits are worth carrying. Exposure is assigned by residential district, not by where a person actually spent the day, which blurs the measurement towards the null rather than away from it. And the outcome is an emergency admission — the severe end of urinary tract infection. Milder infections treated in a clinic are invisible here, so the 4,436 cases are the tip of whatever the real seasonal pattern is.

Sources

  1. 1

    Park J, Lee W, Kang D, Min J, Jang H, Kang C, Kwon D, Kwag Y, Ha E

    Summer temperature and emergency room visits due to urinary tract infection in South Korea: a national time-stratified case-crossover study

    BMC Public Health 2024;24(1):2274

    doi:10.1186/s12889-024-19454-1 · PMID:39169278

    https://doi.org/10.1186/s12889-024-19454-1