Arapahoe County reports 38 pertussis cases and a West Nile-positive mosquito pool
The county’s October report also documents a West Nile diagnosis in a resident and outlines ways to reduce the risk of both diseases.
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Arapahoe County Public Health’s Oct. 14 report listed 38 pertussis cases in 2026 and one mosquito pool carrying West Nile virus, collected in Aurora’s Del Mar neighborhood.
The report listed 60 county pertussis cases in 2024 and 81 in 2025. It said local cases followed a trend similar to Colorado’s statewide increase since fall 2023.
The county’s mosquito-trapping season ended during the week of Sept. 14. Staff collected 3,930 mosquitoes, including 1,100 Culex mosquitoes, which the report identifies as the primary West Nile virus vector. The positive pool came from the Del Mar site during the final week of trapping. The county also reported one resident diagnosed with West Nile virus, but said human cases cannot be attributed to a specific county location.
Vaccination is the best way to prevent pertussis, the Colorado Department of Public Health and Environment says. Its recommendations include routine childhood doses of diphtheria, tetanus and acellular pertussis (DTaP) vaccine; a tetanus, diphtheria and acellular pertussis (Tdap) dose at ages 11–12; Tdap during every pregnancy, preferably between weeks 27 and 36; and a dose for adults who have never received Tdap.
To reduce West Nile risk, the state advises using insect repellent according to its label, wearing long sleeves and pants, limiting outdoor activity around dusk and dawn, draining standing water, and maintaining window and door screens, according to its prevention guidance.