Lab Matters Spring 2019 - Page 28

INFECTIOUS DISEASES MeVA Assay Aids Public Health Labs in Fight Against Measles by Alisa Bochnowski, senior specialist, Respiratory Diseases Almost 20 years after measles was declared eradicated, outbreaks of the virus continue to plague the United States. International travel to areas where the virus remains endemic coupled with communities with low vaccination rates have led to hundreds of infections over the last decade and, subsequently, additional testing assistance from public health laboratories. With the number of confirmed cases currently surpassing pre-eradication declaration levels—and still rising—a new assay has given public health laboratories a new tool in the fight against the spread of the disease. Rash or Reaction? Measles vaccination of vaccine naïve individuals is an important part of curbing an outbreak; however, approximately 5% of individuals vaccinated with a measles- containing vaccine develop clinically indistinguishable symptoms from measles infection (e.g., fever, rash). The routinely used measles virus reverse transcription PCR (RT-qPCR) assay (MeV) cannot distinguish between wild-type infection and vaccine reaction, and sequencing, which could delineate between wild-type and vaccine associated rash, can take up to 72 hours to yield results. To assist in the rapid differentiation between the two, CDC developed the Measles Virus genotype A RT-qPCR (MeVA) based on the detection of genotype A nucleoprotein regions that are unique to the vaccine. This assay was adopted by the Vaccine Preventable Disease Reference Centers in 2018 and used for testing during outbreaks in New York, Washington and Texas. The reference center in Minnesota recently employed the MeVA assay in the case of a child from Minnesota that received the MMR vaccine and then traveled internationally. After returning home to Minnesota, the child began 26 LAB MATTERS Spring 2019 exhibiting symptoms that raised the suspicion of measles three weeks post- vaccination. Because of the recent travel and the vaccination history, the clinician wanted to rule out wild-type measles infection. At the Minnesota Department of Health, they first ran the MeV assay, which resulted in a late positive (Ct score ~38). Attempts to genotype this specimen would likely have been indeterminate since the sensitivity of the genotyping assay decreases in specimens with Ct scores higher than 34 and genotyping would have pushed the result reporting back 24-72 hours. Minnesota was able to run the MeVA assay, which was indeterminate, and combined with early lab data and epidemiological case investigation make a determination to treat the rash as unrelated to either measles or the vaccine. Speeding Results for Treatment Not only does the MeVA assay cut down on time to diagnosis, it can also spare patients from unnecessary medical treatments and the public from panic. During a 2017 outbreak of measles in Washington, the delay in genotyping confirmation resulted in two pregnant women being given IVIG after exposure to individuals who ended up having vaccine- associated rashes, not wild-type cases. Had MeVA been available, these pregnant women would not have been treated with IVIG. In another instance in Washington, a person with a vaccine-associated rash was reported to the media as a suspect measles case due to concern about multiple exposure sites. The public health system had to mitigate public concern and respond to this case for several days before the rash was confirmed as vaccine related. During the current outbreak of measles in Washington and Oregon, the MeVA assay is being used to differentiate between wild-type and vaccine associated rashes saving individuals from Did you know? You can request MeVA testing when submitting specimens to the reference centers for testing. By directly requesting MeVA and supplying patient vaccination history you can help identify the correct diagnostic method and expedite testing. Please contact infectious.diseases@aphl.org for more information. unnecessary medical treatments and the public from unwarranted concern. Sociopolitical trends coupled with a high incidence of disease abroad indicate that measles will continue to be an ongoing public health issue in the United States. Every measles outbreak affects the entire public health infrastructure, but the availability of the MeVA assay provides a new tool to help public health officials and clinicians make informed decisions and to appropriately allocate resources during outbreaks. n PublicHealthLabs @APHL APHL.org