Peter Wehrwein

Peter Rabinowitz, MD, MPH, discusses how climate change, 

How Climate Change Impact Is Changing Infectious Disease Patterns

This article first appeared in our sister brand, 

Warmer weather and the sharp ups and downs of wetter conditions from floods and hurricanes and drier conditions from drought are changing where and when certain infectious diseases occur — and clinicians need to be on the lookout for them, says Peter Rabinowitz, MD, MPH, a professor of environmental and occupational health sciences and director of the University of Washington School of Public Health Center for One Health Research in Seattle. Rabinowitz was a speaker at 2 sessions on climate change year at the 2024 ID Week meeting in Los Angeles, California, held from October 16 -20, 2024.

Rabinowitz, who trained as a family physician, said it is essential for clinicians to know how climate change alters infectious diseases. As the climate becomes more volatile, diseases not typically seen in certain areas may start to occur and become common.

For example, warmer weather will mean an increase in some areas of mosquito-borne diseases, such as dengue fever, Zika, and chikungunya, Rabinowitz said in an interview with 

Rabinowitz told MHE that wet conditions after flooding from hurricanes and other extreme weather events are likely to make leptospirosis more common

 Leptospira bacteria cause leptospirosis in animals' urine, and flood waters can become contaminated with the urine of infected animals.

 altering the who, where, and when of infectious diseases. They can change the range of ticks and, therefore, the risk of tick-borne disease, said Rabinowitz, who is also codirector of UW Alliance for Pandemic Preparedness. 

He noted that extensive periods of dry weather can also mean the emergence of dust-borne diseases, such as Valley fever. Valley fever, also called coccidioidomycosis, is a lung infection caused by inhaling the spores from the 

 fungus that lives in the soil in dry areas of the US.

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Peter Rabinowitz, MD, MPH, discusses how climate change, including extreme weather and temperature shifts, is reshaping the spread of infectious diseases like dengue, leptospirosis, and Valley fever.


The innumerable problems with health care systems in the United States and the rest of the world that were exposed by COVID-19 continue to keep medical investigators busy. They are finding yet more dimensions to the pandemic that has stomped about since March 2020.

At the beginning of the pandemic, experts struggled to understand just how the SARS-CoV-2 virus spreads: by droplets or particles? But that might not be the right question.

In a review published in November 2021 in the 

 Michael Klompas, MD, MPH, an infectious disease expert and a professor of population medicine at Harvard Medical School in Boston, Massachusetts, and his colleagues argue that division of droplet and aerosol transmission is misguided and needs to be retired.

There are viruses such as influenza and mumps that spread by relatively large droplets produced by coughing and sneezing and that fall to the ground relatively quickly. Doctors, nurses, and other clinicians are advised to wear face masks to block the droplets.

Other pathogens are aerosolized, spreading via minute respiratory particles that individuals produce when they talk and breathe. Aerosols tend to stay suspended in the air for much longer periods of times than droplets and travel much farther.

® pointed out in October 2020, perhaps the best analogy for COVID-19 would be how cigarette smoke can linger and spread in an enclosed setting such as a bar (back when smoking was allowed in those establishments).

 In such a situation, 6-foot social distancing offers very little protection.

Measles and tuberculosis are 2 examples of viruses that spread this way. Precautions against aerosols include N95 masks, negative-pressure rooms, ventilation, and high-efficiency particulate air (HEPA) filters.

Klompas et al argue that research into COVID-19 and the SARS-CoV-2 virus demonstrates that individuals generate the full range of respiratory particles, not just either droplets or aerosols. Aerosolized droplets can stay aloft for long periods, and respiratory viruses are not picky about the size of particle that they hitch a ride on. However, aerosols may account for most transmission, partly because individuals produce aerosols just by talking and breathing.

The governing factor of transmission, wrote Klompas et al, is infectious dose—the amount of virus an individual is exposed to. Infectious dose is a product of time and exposure concentration, or how much virus is in the air, the authors wrote. Poor ventilation can allow virus-laden aerosols to accumulate and increase the exposure concentration and, as a result, the infectious dose. Good ventilation, HEPA filters, and ultraviolet disinfection can decrease the amount of virus floating in the air.

Source strength—or how much virus an infected individual is spewing into the air in respiratory particles—is another factor in the complicated question, the authors explained.

Klompas et al discussed some of the implications of the current understanding of respiratory virus transmission for infection control policies and programs. Here is their list of potential policy responses, which was included in the 

Consider creating a uniform set of respiratory precautions for all respiratory pathogens rather than differentiating between airborne vs droplet pathogens.

Consider using higher-level respiratory protection (eg, N95 respirators) in the care of all patients with active respiratory viral infections.

Allocate airborne-infection isolation rooms for pathogens historically associated with long-range transmission and for patients with high viral loads.

Reinforce minimum ventilation standards for nonclinical spaces.

Consider using higher-level respiratory protection such as N95 respirators for all prolonged, face-to-face encounters when the community incidence of SARS-CoV-2 is high.

Consider retiring aerosol-generating procedures.

Diamond F. Q&A: hospital ventilation designed to thwart COVID. 

®. December 29, 2020. Accessed December 9, 2021. https://www.infectioncontroltoday.com/view/q-a-hospital-ventilation-designed-to-thwart-covid

Klompas M, Milton DK, Rhee C, Baker MA, Leekha S. Current insights into respiratory virus transmission and potential implications for infection control programs: a narrative review. 

. Published online November 9, 2021. doi:10.7326/M21-2780

Diamond F. Smoke gets in your eyes: how COVID spreads indoors. 

®. October 6, 2020. Accessed December 9, 2021. https://www.infectioncontroltoday.com/view/smoke-gets-in-your-eyes-how-covid-spreads-indoors

Articles

Recent research into COVID-19 suggests that health care systems need to move beyond the idea that pathogen spread happens either via droplets or aerosolized particles. Patients can generate the full range of respiratory particles.

Peter Wehrwein

Articles

How Climate Change Impact Is Changing Infectious Disease Patterns

COVID-19 Spread: Droplets or Particles? It’s Not an Either/Or