Other Sections of the Report
You can find the rest of the report in the following links:
About the 2025 Regional Climate Health Monitoring Report RCHMR Extreme Heat Extreme Cold Air Quality Mental HealthOverview of Climate Change-Related Infectious Diseases
Climate change fuels the spread of infectious diseases, increasing health risks worldwide. Because the life cycles of many germs and pathogens are sensitive to weather, shifting climate patterns directly affect how and where diseases emerge. For example, warmer global temperatures lead to longer summers and milder winters, which makes it easier for disease-carrying mosquitoes and ticks to survive longer and expand into new regions. Similarly, changes in rainfall and more frequent extreme weather events, like floods and droughts, are allowing harmful fungi to thrive in new geographic areas, increasing the occurrence of certain communicable diseases.
In the tri-county region, most disease cases tracked in this Data Story plummeted in 2020 due to the COVID-19 shutdown. Cases then rebounded in 2021 and continued to climb through 2023. From 2023 to 2024, the total number of cases generally decreased, but this varied by condition. While the two most common diseases, Campylobacterosis and Salmonellosis, declined, less common diseases like Tuberculosis (TB), Coccidioidomycosis (Valley fever), and Lyme disease increased slightly.
References
[1] Centers for Disease Control and Prevention (2025). Climate and Infectious Diseases. Accessed at: https://www.cdc.gov/ncezid/topics-programs/climate-infectious-disease.html.
[2] Semenza JC, Rocklöv J, and Ebi KL. Climate Change and Cascading Risks from Infectious Disease. Infect Dis Ther 11, 1371–1390 (2022). https://doi.org/10.1007/s40121-022-00647-3.
Communicable Diseases
Climate change influences the survival, reproduction, and adaptation of microorganisms that carry disease. Some climate events, such as extreme heat or flooding, increase the growth of disease-causing microbe populations, as well as human exposure and the risk of infection through contaminated food, water, and water-based recreational activities. Changes in temperature and rainfall in the Pacific Northwest are projected to create conditions that promote the growth of disease-causing microbes.
Salmonellosis: Increase in temperature is directly associated with an increased number of reported Salmonellosis cases. Studies have estimated an increase of 1.2% in the relative risk of Salmonellosis for every degree increase in weekly temperature. Salmonella species multiply faster in warmer temperatures, which leads to an increased risk of food contamination during processing, storage, and production. The number of cases is typically higher during summer months, with an increased risk of severe illness among children under five years and those over 65 years.
Campylobacterosis (Campy): The intestinal bacteria Campylobacter shows a seasonal pattern peaking in the summer months. Warmer conditions promote the growth of bacteria in raw sewage, increasing the risk of exposure. Heavy rains and floods can lead to sewage overflow, also increasing the risk of exposure.
Tuberculosis (TB): Climate change can affect the spread of TB disease by displacing people through drought, landscape change, rising sea levels and natural disasters. The spread of TB increases when people are displaced or forced to migrate from regions where TB is common and relocate to places with low rates of the disease. Famine and changes in environmental conditions can also spread TB by lowering a person’s immunity and increasing their susceptibility to infections.
Elevating Equity
Low income and rural areas are impacted more by communicable diseases resulting from climate change and environmental factors. People with lower incomes have fewer resources and live in areas less equipped to mitigate the fallout from extreme heat, floods from precipitation, and other extreme weather conditions compared to higher income individuals. Groups that are at higher risk of communicable diseases include:
- Older adults, children, pregnant people and those with compromised immune systems.
- Communities of color that have experienced historic redlining, structural exclusion, or who have lived in areas that have not been prioritized for public works enhancements.
- People who spend time in water bodies for recreation or occupation.
- People living in communities with aging water and sewage infrastructure that may be more prone to flooding and water contamination.
- Communities that are geographically isolated or do not have backup systems for essential services like water when those systems are damaged by extreme weather
Trends
Campylobacterosis
Salmonellosis
Tuberculosis
References
Semenza JC, Herbst S, Rechenburg A, et al. Climate Change Impact Assessment of Food- and Waterborne Diseases. Crit Rev Environ Sci Technol. 2012;42(8):857–890.
Greer A, Ng V, Fisman D. (2008) Climate change and infectious diseases in North America: the road ahead. Canadian Medical Association Journal 178 (6) 715-722.
Haggerty B, York E, Early-Alberts J, Cude C. Oregon Climate and Health Profile Report. Oregon Health Authority. September 2014: Portland, OR.
Fleur M, Charron DF, Holt JD, Allen OB, and Maarouf AR. (2006) A time series analysis of the relationship of ambient temperature and common bacterial enteric infections in two Canadian provinces. Int. J. Biometeorol. 50, 385–391.
Lake IR, Gillespie IA, Bentham G, Nichols GL, Lane C, Adak GK, and Threlfall EJ. (2009) A re-evaluation of the impact of temperature and climate change on foodborne illness. Epidemiol. Infect. 137, 1–10.
Vector-Borne and Fungal Infections
Vector-borne diseases are illnesses transmitted to humans by an insect that feeds on blood. Ticks and mosquitoes are major vectors in the tri-county region. Climate change influences the habitat, survival, and seasonality of these insects. Increases in regional temperatures also expand the environments suitable for fungi to live, and more extreme weather events like windstorms and wildfires can help release spores from the soil into the air and distribute to wider geographies. Fungal infections can lead to mild symptoms, like skin rashes, or more serious reactions like lung inflammation.
Lyme Disease: Lyme disease is a bacterial infection spread by tick bite. Symptoms include headache, fever, and a characteristic target-like rash known as erythema migrans. It is most common in the northeast region of the United States, however, it is also present in the tri-county region in Oregon. Tick activity is sensitive to temperature, precipitation, and humidity, all of which are affected by climate change. The tick life cycle is guided by changes in seasons. Ticks begin looking for a host in spring and summer. As spring and winter temperatures increase, ticks begin to look for a host earlier, increasing the length of the Lyme disease season and the number of potential cases.
West Nile Virus: While rare, West Nile Virus are transmitted by mosquitoes, who reproduce more in hotter and humid conditions. Warmer weather expands mosquito habitat and extends their season of activity earlier in the summer and later into the fall. Mosquitoes bite more in warmer temperatures, increasing the risk of vector-borne disease transmission.
Coccidioidomycosis: Also known as Valley Fever, Coccidioidomycosis is a lung infection caused by a fungus that lives in soil. Symptoms include cough and fever. A small percentage of infections are more severe and require anti-fungal treatment. However, it is also common to experience no symptoms at all, which suggests the current disease burden is an underestimate. The fungus typically is found in dry, arid regions in the southwest. The combination of expanding drought areas and wind are possible contributing factors to the expansion of areas in which the fungus is found.
Multnomah County Environmental Health Vector team surveillance shows proliferation of adult mosquito population since 2020.
Elevating Equity
Exposure and vulnerability to the risk of insect bites is largely the outcome of social and environmental factors. The conditions that someone lives or works in shape exposure patterns. Groups that are at a higher risk of vector-borne disease include:
- Outdoor workers near habitats supporting insect breeding (e.g., construction, landscape design, landscaping, agriculture).
- People experiencing houselessness with no shelter from insect exposure.
- People living in housing without window or door screens and other sufficient barriers to exclude insects, including renters without tenant protections or whose landlords allow unsafe conditions.
- Youth, older adults, and people with immune conditions are more susceptible to severe illness from vector-borne diseases.
- People without means to purchase personal protective repellants or who lack access to educational resources about insect bite prevention.
Trends
Coccidioidomycosis
Lyme Disease
West Nile Virus
Cases have been sporadic in the region, with one recorded in 2014, 2018, and 2023.
References
Williams SL, Toda M, Chiller T, Brunkard JM, & Litvintseva AP (2024). Effects of climate change on fungal infections. PLOS Pathogens, 20(5), e1012219. https://doi.org/10.1371/journal.ppat.1012219
Centers for Disease Control (2024). About Lyme Disease. Accessed at: https://www.cdc.gov/lyme/about/index.html
Oregon Health Authority. (2017). Lyme Disease in Oregon. Public Health Division. Accessed at: https://www.oregon.gov/oha/PH/DISEASESCONDITIONS/COMMUNICABLEDISEASE/VETERINARIANS/Documents/DiseaseFactsheets/lyme.pdf
Deshpande G, Beetch JE, Heller JG, Naqvi OH, & Kuhn KG (2023). Assessing the Influence of Climate Change and Environmental Factors on the Top Tick-Borne Diseases in the United States: A Systematic Review. Microorganisms, 12(1), 50. https://doi.org/10.3390/microorganisms12010050
Paz S (2015). Climate change impacts on West Nile virus transmission in a global context. Philosophical Transactions of the Royal Society B: Biological Sciences (370) 1-11.
Beard CB, Eisen RJ, Barker CM, Garoalo JF, Hahn M, Hayden M, Monaghan AJ, Ogden NH, and Schramm PJ (2016). Ch.5: Vector Borne Diseases. The Impacts of Climate Change on Human Health in the United States: A Scientific Assessment. U.S. Global Change Research Program, Washington, DC, 129–156.
Centers for Disease Control. (2024). About Valley Fever. Accessed at: https://www.cdc.gov/valley-fever/about/index.html
Williams SL, Benedict K, Jackson BR, Rajeev M, Cooksey G, Ruberto I, Williamson T, Sunenshine RH, Osborn B, Oltean HN, Reik RR, Freedman MS, Spec A, Carey A, Schwartz IS, Medina-Garcia L, Bahr NC, Kuran R, Heidari A, Toda M (2025). Estimated Burden of Coccidioidomycosis. JAMA Network Open, 8(6), e2513572. https://doi.org/10.1001/jamanetworkopen.2025.13572.
Crum NF (2022). Coccidioidomycosis: A Contemporary Review. Infectious Diseases and Therapy, 11(2), 713–742. https://doi.org/10.1007/s40121-022-00606-y
Bardosh KL, Ryan SJ, Ebi K, Welburn S, Singer B. Addressing vulnerability, building resilience: community-based adaptation to vector-borne diseases in the context of global change. Infect Dis Poverty. 2017 Dec 11;6(1):166. doi: 10.1186/s40249-017-0375-2. Erratum in: Infect Dis Poverty. 2018 Jan 30;7(1):5. doi: 10.1186/s40249-018-0387-6. PMID: 29228986; PMCID: PMC5725972.