Mapping the Risk for Measles Outbreaks in the US: Public Health Watch
International travel and poor vaccine uptake are among the key factors identified by investigators who mapped counties at-risk for measles cases in the United States.
Talk about unintended consequences.
An analysis by an international team of researchers published in The Lancet Infectious Diseases confirms 2 widely held opinions regarding the key contributing factors behind recent outbreaks of measles: that reduced vaccine uptake due to nonmedical exemptions and the reintroduction of the virus via foreign travel have helped fuel the disease’s resurgence. Unfortunately, the data have been made public at a time when reports of bias crimes against members of Orthodox Jewish communities in New York, which officials believe have been “inspired” by ongoing measles outbreaks in Brooklyn and Rockland County, are on the rise.
“I am very concerned [about these reports],” analysis co-author Sahotra Sarkar, PhD, a professor at the University of Texas-Austin, told Contagion®. “In the interest of public health, we have to perform these analyses and make them public, but how to guard against such a response is a major challenge.”
Sarkar, a self-described “philosopher of science,” naturally goes beyond the data in much of his work, which is geared toward a humanities-based approach to medicine and health. With that in mind, he and his colleagues have developed a quantitative model designed to identify the US counties “with the highest risk of a measles outbreak in 2019.” Their “spatial relative risk profile” for each of these regions is based on 4 factors: international air travel volume, nonmedical vaccine exemption rates, population, and incidence of measles at travel origin.
“Measles is not a vector-borne disease, obviously, but nevertheless it is influenced by spatial epidemiology,” Sarkar explained. “We tend to see it more often in areas with higher densities of people and it travels from place to place.”
According to the US Centers for Disease Control and Prevention (CDC), at least 45 US counties have reported measles cases thus far in 2019—and, notably, 30 of them appear in either the top 25 “at-risk” list developed by Sarkar and colleagues, or are located geographically adjacent to counties included on that list. For example, Kings County, Washington, where officials recently announced the sixth confirmed case of measles, is ranked fifth among at-risk counties.
In addition, although the county that Brooklyn lies in doesn’t make the rankings, the borough is adjacent to Queens County, which, with a relative risk of 0.293, sits fourth on the list. Cook County (Illinois), Los Angeles County (California), and Miami-Dade County (Florida) are ranked first, second, and third, respectively.
Interestingly, this is not the first time the team has developed a seemingly accurate predictive model for disease transmission. In 2016, the same authors published a similar analysis for Zika virus risk in the United States, which accurately predicted outbreaks of the mosquito-borne virus in Florida and Texas and was published in The Lancet Infectious Disease.
However, as with the Zika analysis, the goal of their work in measles is not to incite panic or bring unwanted attention to a particular demographic, but rather to raise awareness of the geographic and population factors related to disease transmission in order to educate the public and focus health outreach efforts. Indeed, Sarkar is part of a team developing a public health curriculum that will teach students “how to approach public policy and lobbying so that they can make a difference” in how infectious diseases are managed by governments, he said.
“In general we have been using these results and our other work to fight the rise of the antivaccine movement—among the major health problems of the 21st century,” he added. Noting further that he recently published a commentary in his local paper, the Statesman, as part of these efforts, he indicates that controversial antivaxxer Andrew Wakefield is now based in Austin, and his influence there has led to reduced MMR vaccine uptake in the community. “I have also been urging states to get rid of all nonmedical vaccine exemptions, including religious exemptions.”