WEST TEXAS — The Pan American Health Organization (PAHO) will determine in November whether the United States maintains its measles-free designation. This decision follows a prolonged measles outbreak that began in West Texas and subsequently spread nationally, with evidence suggesting continuous domestic virus transmission.
Measles cases have since been reported in nearly all U.S. states. Two unvaccinated girls in Texas and an adult in New Mexico died from the outbreak. The Texas outbreak appeared to decline in July of the previous year, but measles cases later emerged in Utah.
Measles infections in Utah increased during the fall and winter and continued into May. Utah State Epidemiologist Dr. Leisha Nolen stated that a review of the first confirmed patient's travel history and contacts could not identify the infection source. Evidence suggests the virus was circulating undetected in Utah prior to this confirmed case. Related measles viruses infected residents of Utah through May.
The United States must demonstrate that measles did not spread endemically within the country for more than one continuous year to retain its measles-free designation. The Centers for Disease Control and Prevention (CDC) is analyzing the full genetic code of measles viruses from infected patients. In November, the former leader of the CDC stated that preliminary genomic analysis indicated the Utah measles cases were not directly linked to the Texas cases. A Department of Health and Human Services spokesperson stated that initial sequencing work was performed by state laboratories and the agency is conducting a more comprehensive investigation.
Genetic analysis shows only twelve genetic letters differ between the initial Texas virus sample and a Utah virus sample collected over a year later. A mutation changing a guanine molecule to an adenine molecule appeared in the virus weeks after the Texas outbreak began. A Texas virus sample collected in May contained five distinct mutations. Those same five mutations appeared in a Utah virus sample collected in June. The five-mutation pattern was also identified in virus samples from patients in Iowa, North Dakota, Minnesota, and Alaska from May and June of the specified year.
PAHO invited the United States to present its case regarding the virus spread in April. American health officials requested additional time to investigate the virus spread, which delayed the review to November. Daniel Salas, a PAHO official, said, "What the U.S. is trying to do with this whole genome sequencing is trying to find some patterns that could eventually say, for example, this mutation of the virus occurred in a different country, in a different place to the current outbreak that they're trying to analyze, so that eventually, that might be taken into consideration to somehow replace the epidemiological information that is missing. There's no country that has done this before."