Arapahoe County reports 38 whooping cough cases and West Nile virus in a mosquito pool
The county’s October report also says three mobile vaccination clinics served schools with low vaccine compliance.
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Arapahoe County Public Health reported 38 pertussis cases in 2026 and one mosquito pool carrying West Nile virus, collected in Aurora’s Del Mar neighborhood, in its Oct. 14 report.
The report listed 60 county pertussis cases in 2024 and 81 in 2025. It said local cases followed a statewide increase that began in fall 2023.
The report also said the county’s Immunization Program held three mobile clinics at schools identified as having low vaccine compliance, providing on-site vaccination services to students with documented barriers to care. It did not specify which vaccines the clinics offered.
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 vector for West Nile virus. 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.