A recent measles outbreak in South Carolina has grown by two cases, according to health officials in the state, as the US outbreak total has reached 1,563 cases, the most in decades. 

Seven measles cases have been reported in Spartanburg County, South Carolina, since Sept. 25, and the state has had 10 total cases this year. The current outbreak has no identified source, which suggests measles is circulating in the community. 

In Muskegon County, Michigan, officials reported a second measles case with a possible exposure at an urgent care clinic. Michigan has now had 28 measles cases this year. 

CDC: 19 more US cases 

Today the Centers for Disease Control and Prevention (CDC) updated its measles data for the country, showing a total of 1,563 cases in 2025, an increase in 19 cases since last week. This is the most cases seen in the United States since 2000, the year measles was officially declared eliminated. 

Twenty-seven percent of cases have been in children under the age of 5, and 92% of patients are unvaccinated or have an unknown vaccination status. CDC officials have confirmed 44 outbreaks, which account for 87% of confirmed infections.

Researchers are calling for revision of the World Health Organization pertussis (whooping cough) case definition after finding that both it and a modified definition miss many lab-confirmed cases in preschoolers. 

Investigators from the National Institute for Communicable Diseases (NICD) in South Africa examined national respiratory-illness sentinel surveillance data on children younger than 5 years from 2017 through 2023. 

Data were from outpatients with influenza-like illness (ILI) and hospitalized patients with severe respiratory illness (SRI). Nasopharyngeal swabs were tested for Bordetella pertussis (the bacterium that causes pertussis) using polymerase chain reaction (PCR). Investigators then compared sensitivity, specificity, and case-definition performance indicators with the PCR results.

"Pertussis is vaccine-preventable, and surveillance can guide interventions," the researchers noted. "Assessing the performance of syndromic surveillance and the World Health Organization (WHO) pertussis case definitions can identify improvements to enhance detection and monitoring of Bordetella pertussis."

The findings were published yesterday in the Journal of Infectious Diseases.

Modified definition improved sensitivity, lowered specificity

Among 23,642 participants with PCR results, B pertussis was detected in 30 of 4,125 (0.7%; median age, 6.2 months) patients with ILI and 314 of 19,517 (1.6%); median age, 1.7 months) patients with SRI.

Revising the WHO pertussis case definition and integrating pertussis into syndromic surveillance could improve detection while leveraging existing resources.

Of 4,125 participants with ILI, 90.4% met the NICD ILI case definition, and 24.4% met the modified WHO definition. Among the 30 PCR-positive B pertussis cases in ILI, 63.3% met the NICD ILI definition, and 43.3% met the modified WHO definition, with 6.7% meeting both.

Compared with the WHO pertussis case definition, a modified definition including apnea (pauses in breathing) and omitting cough duration improved sensitivity (ILI, 30.0% vs 43.3%; SRI, 55.7% vs 60.2%) but lowered specificity (ILI, 90.5% vs 75.8%; SRI, 88.3% vs 80.9%).

Negative predictive values were over 99% for both definitions, but positive predictive values were less than 15%, reflecting low prevalence. Both the WHO and modified pertussis case definitions missed a large percentage of pertussis cases (ILI, 70.0% vs 56.7%; SRI, 44.3% vs 39.8%).

"Revising the WHO pertussis case definition and integrating pertussis into syndromic surveillance could improve detection while leveraging existing resources," the authors concluded.

• Mexican health officials have confirmed 3 new human cases of New World screwworm in the past week, for a cumulative total of 55. The parasitic fly usually infects cattle, but it can lay eggs on humans. Infestations can be serious and lead to sepsis if untreated, but are not contagious.
• The US Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) reported a newly confirmed H5N1 avian flu outbreak in commercial turkeys in Ottawa County, Michigan, involving 30,000 birds. This is the first detection of highly pathogenic avian influenza in Michigan since January. A backyard flock in Beaverhead, Montana of 40 birds was also confirmed to have H5N1.
• The European Centre for Disease Prevention and Control (ECDC) today released updated data on West Nile virus activity on the continent. So far this year 13 countries in Europe have reported 989 locally acquired cases, 714 of which (72%) are in Italy.