Mohave County reports measles outbreak, pertussis spike centered in Colorado City area

Anna Scherzer, epidemiologist for Mohave County, presented communicable-disease surveillance data through Sept. 30, 2025 and provided updated outbreak information to the board.

Scherzer said surveillance shows higher-than-typical influenza and RSV counts this season, increased reports of invasive streptococcal disease (group A and pneumococcal invasive disease), and a pertussis cluster largely centered in the Colorado City service area. She reported that most pertussis cases (about 90 percent) were unvaccinated and that several cases required hospitalization. Scherzer said the county had passed two incubation periods without additional Colorado City pertussis cases at the time of reporting, indicating containment of that cluster but noting the potential for additional reports to trickle in.

On measles, Scherzer reported that the first laboratory-confirmed case the county received was reported in mid-August and that, as of Oct. 16, the department had identified 74 measles cases in Mohave County residents; Utah jurisdictions across the state line also reported substantial case counts. Measles cases were overwhelmingly among persons without a valid MMR dose (presenter: 99 percent unvaccinated at the time of the Oct. 16 memo). Scherzer noted two hospitalized Arizona residents linked to the outbreak. She explained basic clinical features and the long incubation period (up to 21 days) and warned that measles is infectious for four days before rash onset and four days after rash appearance, which complicates outbreak control.

Board members asked clarifying questions about immunity (measles confers lifelong immunity after infection) and pertussis boosters; Scherzer explained that pertussis immunity wanes and boosters are recommended for adults in certain circumstances. Commissioners also asked about cryptosporidium and giardia reports and whether any water-source outbreak was identified; Scherzer said the cryptosporidium reports were not tied to a single source and giardia remains an intermittent, ongoing detection.

The board accepted the routine summary of reportable diseases for 01/01/2025''to 09/30/2025 by motion and vote earlier in the meeting. Scherzer and board members emphasized the public-health burden of vaccine-preventable illnesses and the operational strain of prolonged incubation periods for measles.