Climate Change and the Internist's Practice: Understanding the Impact of the Environment on the Diseases We Treat Every Day

Dr Neeraj Manikath , claude.ai

Abstract

Climate change represents one of the most significant public health challenges of the 21st century, fundamentally altering the epidemiology of diseases encountered in internal medicine practice. This review examines the direct and indirect health impacts of climate change on patients with chronic diseases, the shifting geography of infectious diseases, and practical strategies for climate-aware clinical practice. As internists, we must recognize that the examination room is no longer isolated from environmental conditions outside—our patients' diseases are increasingly shaped by rising temperatures, changing precipitation patterns, and deteriorating air quality.

Introduction

The relationship between climate and human health is neither new nor theoretical. However, the acceleration of anthropogenic climate change over the past several decades has created unprecedented challenges for medical practice. Global temperatures have risen approximately 1.1°C since pre-industrial times, with projections suggesting increases of 1.5-2°C within the next two decades even under optimistic scenarios.Recent data indicates that climate-sensitive health risks are expanding rapidly, with vector-borne diseases spreading to previously unaffected regions and heat-related mortality increasing substantially among vulnerable populations.

For internists, climate change is not a distant threat but a present reality affecting our daily practice. Patients with cardiovascular disease, respiratory conditions, diabetes, and renal disease face heightened risks during extreme weather events. The geographic distribution of infectious diseases we learned in medical school is becoming obsolete. This review provides evidence-based guidance for recognizing and managing climate-related health impacts in internal medicine.

The Changing Map of Infectious Disease

Geographic Expansion of Vector-Borne Diseases

The distribution of vector-borne diseases is fundamentally determined by climate, as arthropod vectors require specific temperature and humidity ranges for survival and reproduction. Warming temperatures have enabled the expansion of tick populations northward and to higher elevations, with Ixodes scapularis now established in regions of Canada where it was previously absent.

Lyme Disease: Lyme disease cases in the United States have more than doubled since the 1990s, with endemic areas expanding from the Northeast into the Upper Midwest and parts of the Mid-Atlantic and Southeast. The tick vector Ixodes scapularis now thrives in regions where winter temperatures previously limited its survival. Counties reporting Lyme disease have increased substantially, and the disease is increasingly recognized in areas historically considered non-endemic.

Clinical Pearl: When evaluating patients with unexplained fever, arthralgia, or neurological symptoms, inquire specifically about outdoor activities and tick exposure, even in regions not traditionally endemic for Lyme disease. Consider Lyme disease in the differential diagnosis for patients presenting with Bell's palsy, unexplained carditis, or migratory arthritis.

Valley Fever (Coccidioidomycosis): This fungal infection, caused by Coccidioides species endemic to the southwestern United States, is expanding its range. Changing precipitation patterns and increased dust storms have contributed to rising incidence rates, with cases now reported in areas of Washington, Montana, and other previously non-endemic regions. The fungus thrives in arid soil and becomes airborne during dust storms or soil disturbance.

Clinical Hack: For patients with community-acquired pneumonia in endemic or emerging areas who fail to respond to standard antibiotic therapy, order coccidioidal serologies. Consider empiric antifungal therapy in immunocompromised patients from endemic areas presenting with pneumonia, as disseminated disease carries significant mortality.

Mosquito-Borne Diseases: Dengue fever transmission zones have expanded significantly, with the geographic range of Aedes aegypti and Aedes albopictus mosquitoes now including parts of the southern and southeastern United States. Local transmission of dengue has been documented in Florida and Texas with increasing frequency. West Nile virus has become established throughout North America, with case numbers fluctuating based on temperature and precipitation patterns that affect mosquito populations.

Oyster: When evaluating patients with acute febrile illness following travel to tropical regions or residence in southern states, maintain high suspicion for dengue fever, particularly during late summer and fall. The classic triad of fever, severe headache with retro-orbital pain, and myalgias ("breakbone fever") should prompt testing even in areas not traditionally considered endemic.

Waterborne Disease Risks

Rising temperatures and changing precipitation patterns affect waterborne disease transmission. Vibrio vulnificus infections associated with warming coastal waters have increased, with cases now occurring in northern regions where the bacterium was previously unable to survive. Heavy rainfall events and flooding can overwhelm water treatment systems, increasing risks of cryptosporidiosis, giardiasis, and other enteric infections.

Heat-Related Illness and Chronic Disease

Disproportionate Impact on Vulnerable Populations

Heat waves are increasing in frequency, duration, and intensity worldwide, with profound implications for patients with chronic diseases. Extreme heat affects thermoregulation, cardiovascular function, renal perfusion, and metabolic control, creating a perfect storm for patients with pre-existing conditions.

Congestive Heart Failure (CHF): Patients with CHF face multiple heat-related challenges. High ambient temperatures increase cardiac workload through peripheral vasodilation and increased heart rate. Dehydration concentrates the blood, increasing afterload. Studies have demonstrated increased hospitalizations for heart failure during heat waves, with mortality rates rising significantly when temperatures exceed local 95th percentile thresholds.

Clinical Pearl: Counsel CHF patients to maintain fluid balance during hot weather—not excessive hydration that may precipitate volume overload, but adequate intake to prevent dehydration. Daily weight monitoring becomes even more critical during summer months. Advise patients to limit outdoor activities during peak heat hours (10 AM-4 PM) and ensure access to air conditioning.

Chronic Obstructive Pulmonary Disease (COPD): Heat exacerbates COPD through multiple mechanisms. High temperatures increase ozone formation, directly irritating airways. Heat-related dehydration thickens secretions, impairing mucociliary clearance. Emergency department visits for COPD increase significantly during heat waves, with the risk amplified when high heat coincides with elevated air pollution.

Clinical Hack: Provide COPD patients with action plans specifically for high-heat days: increase inhaled bronchodilator use prophylactically, maintain hydration, use air conditioning with filters, and have a low threshold for initiating prednisone if symptoms worsen. Consider prescribing short courses of prednisone for home use during severe heat waves.

Diabetes Mellitus: Temperature extremes affect glucose metabolism and insulin action. Heat stress impairs glucose tolerance and insulin sensitivity, while dehydration can precipitate hyperglycemic hyperosmolar state. Additionally, insulin and glucose monitoring supplies may be damaged by excessive heat exposure.

Oyster: Educate diabetic patients that blood glucose may be more difficult to control during hot weather. Increase monitoring frequency during heat waves. Insulin should never be stored in cars or direct sunlight—provide specific guidance on storage during power outages. Test strips and continuous glucose monitoring sensors may give inaccurate readings if exposed to excessive heat.

Medication Considerations

Multiple medications commonly prescribed by internists impair thermoregulation or increase heat-related risks. Diuretics promote dehydration and electrolyte disturbances. Beta-blockers and calcium channel blockers impair cardiovascular adaptation to heat stress. Anticholinergics inhibit sweating. Psychotropic medications affect hypothalamic temperature regulation.

Clinical Pearl: Conduct medication reviews specifically focused on heat sensitivity before summer months. Consider temporary dose adjustments of diuretics during heat waves. Educate patients that certain medications increase vulnerability to heat illness, and symptoms like dizziness, weakness, or confusion during hot weather should prompt immediate medical attention.

Air Pollution as a Cardiovascular and Pulmonary Risk Factor

Particulate Matter and Cardiovascular Disease

The relationship between air pollution and cardiovascular disease is now firmly established. Exposure to fine particulate matter (PM2.5) increases risks of myocardial infarction, stroke, arrhythmias, and heart failure exacerbations through systemic inflammation, oxidative stress, and endothelial dysfunction.

Short-term exposure to elevated PM2.5 levels—even for hours—can trigger acute cardiovascular events. Studies have demonstrated that myocardial infarction risk increases within 24 hours of exposure to elevated particulate matter concentrations. Long-term exposure contributes to atherosclerosis progression and increased cardiovascular mortality.

Clinical Hack: Counsel high-risk cardiovascular patients (those with established coronary disease, heart failure, or multiple risk factors) to check daily Air Quality Index (AQI) readings, available through weather apps and epa.gov/airnow. On days with AQI above 100 (orange category or higher), advise limiting outdoor exercise and keeping windows closed while using air filtration if available.

Respiratory Effects Beyond COPD

While COPD patients are particularly vulnerable, air pollution affects all respiratory conditions. Asthma exacerbations correlate strongly with elevated ozone and particulate matter levels, with emergency department visits increasing significantly on high-pollution days. Even individuals without pre-existing lung disease experience decreased lung function with chronic exposure to elevated pollution levels.

Wildfire smoke has emerged as a significant and recurring air quality threat, containing particularly high concentrations of PM2.5 and toxic compounds. Regions thousands of miles from active fires experience air quality degradation sufficient to increase respiratory and cardiovascular hospitalizations.

Oyster: During wildfire smoke events, recommend N95 or KN95 masks for outdoor activities, not just for infectious disease protection. These properly fitted respirators filter particulate matter effectively. Surgical masks provide minimal protection against smoke particles. Create indoor clean-air spaces using portable HEPA filters in bedrooms for vulnerable patients.

Practical Counseling on High-Pollution Days

Integrate air quality counseling into routine care for patients with cardiopulmonary disease:

1. Risk Stratification: Identify high-risk patients (COPD, asthma, CHF, coronary disease, diabetes, elderly) who should receive specific air quality guidance.

2. Action Thresholds: Provide clear instructions based on AQI levels:

   • AQI 0-50 (Green): Normal activities
   • AQI 51-100 (Yellow): Sensitive groups should consider reducing prolonged outdoor exertion
   • AQI 101-150 (Orange): Sensitive groups should reduce prolonged outdoor exertion
   • AQI 151+ (Red or higher): Everyone should avoid prolonged outdoor exertion; sensitive groups should remain indoors

3. Indoor Air Quality: Recommend HEPA air purifiers for bedrooms. During high-pollution events, keep windows closed and set HVAC systems to recirculate rather than bringing in outside air.

4. Exercise Modification: Advise patients that outdoor exercise on high-pollution days carries cardiovascular risks comparable to smoking cigarettes. Recommend indoor exercise alternatives or rescheduling outdoor activities to early morning when pollution levels are typically lower.

Green Prescriptions: Incorporating Nature Exposure and Climate-Aware Counseling

Evidence for Nature-Based Interventions

Emerging evidence supports health benefits of nature exposure. Regular time in green spaces correlates with reduced cardiovascular disease, improved mental health, lower obesity rates, and decreased all-cause mortality. The mechanisms appear multifactorial: increased physical activity, stress reduction, improved air quality in vegetated areas, and possibly beneficial microbial exposures.

Clinical Pearl: Consider "green prescriptions" as legitimate preventive interventions. Recommend specific, actionable nature exposure: "Walk in the park for 30 minutes three times weekly" rather than vague advice to "spend time outdoors." For urban patients without easy park access, even tree-lined streets provide benefits compared to concrete environments.

Climate-Aware Patient Counseling

Internists can incorporate climate considerations into preventive counseling:

Diet: Plant-forward diets benefit both individual health and planetary health. The same dietary pattern that reduces cardiovascular disease risk—emphasizing vegetables, fruits, whole grains, legumes, and nuts while limiting red meat—also reduces greenhouse gas emissions and environmental impact.

Active Transportation: Encourage walking and cycling for transportation when safe and feasible. This provides the dual benefit of physical activity and reduced vehicle emissions.

Heat Preparedness: Develop individualized heat action plans for vulnerable patients before summer, including specific temperature thresholds for modifying activities, hydration strategies, and cooling center locations.

Oyster: Frame environmental health recommendations positively rather than as deprivation. Emphasize personal health benefits first, with environmental benefits as an additional advantage. Patients respond better to "this dietary pattern reduces your heart disease risk and also happens to be environmentally sustainable" than to appeals based solely on climate impact.

Future Directions and the Internist's Role

Climate change will continue reshaping disease patterns for decades regardless of mitigation efforts. Internists must remain informed about emerging infectious disease risks in their regions, recognize early manifestations of heat-related illness in vulnerable patients, and provide anticipatory guidance for environmental health risks.

Medical education must evolve to prepare future internists for climate-related health challenges. Continuing medical education should include updates on changing disease epidemiology and evidence-based climate adaptation strategies.

At the healthcare system level, internists can advocate for climate-resilient infrastructure, including backup power for heat waves and improved air filtration systems. Professional societies should provide leadership in climate health education and policy advocacy.

Conclusion

Climate change represents a fundamental threat to human health, but internists possess unique opportunities to protect patients through recognition of climate-sensitive diseases, anticipatory guidance, and climate-aware clinical practice. The evidence is clear: our patients' health is already affected by environmental changes, and these impacts will intensify. By integrating climate considerations into daily practice, we fulfill our professional obligation to address all factors affecting patient health. The examination room cannot be isolated from the environment outside—it's time to open our eyes to the changing climate and adapt our practice accordingly.

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