Measles outbreaks are continuing in the U.S, with the number of cases already outpacing last year's levels. At the beginning of May, according to the Centers for Disease Control and Prevention (CDC), there were already 764 cases of measles since January 1, 2019. Last year, there were a total of 372 cases. (The number of cases is updated weekly by the CDC.)
In fact, the level of 2019 measles cases is the largest number reported in the U.S. since 1994 and since measles was declared eliminated in 2000. These outbreaks are linked to unvaccinated travelers who are infected abroad in countries such as Israel, Ukraine, and the Philippines, where large measles outbreaks are occurring. When these travelers return to the U.S., they spread the infection mostly to unvaccinated children and adults in their communities. In the U.S., the hardest hit communities include Rockland County in New York State, New York City, Washington State, New Jersey, Butte County and others in California, and Michigan.
Measles is a very contagious viral infection and is easily spread when infected people cough and/or sneeze, dispersing droplets in the air that other people breathe. Measles can also spread when people touch contaminated surfaces (e.g., door knobs, tables) and then touch their face, nose, mouth or eyes. An infected person can spread measles even before they have symptoms (e.g., high fever, cough, runny nose, red and watery eyes, and then a rash that starts on the face and spreads down to the trunk and legs). According to the CDC, nine out of ten people who aren't vaccinated for the disease will get the virus if they come in contact with an infected person.
The CDC recommends two doses of the vaccine to protect against measles as well as mumps and rubella (MMR). Usually children are given the first dose between ages 12 and 15 months and the second dose between ages 4 and 6 years old. Because many American children get the measles vaccine, infections are relatively rare in the U.S., but millions of cases occur around the world.
Many people don't realize how contagious measles is and that it can become a serious infection. While most people recover from measles in a week or so, in some cases, it can lead to complications including pneumonia, permanent brain damage, deafness and even death, according to the CDC. About one to two people out of 1,000 who get measles die. Serious complications primarily affect babies and children but can also occur in adults who never had measles or the vaccine, or whose immunity has waned. There is no treatment for measles other than supportive care (resting and drinking plenty of liquids).
Confirming suspected cases of measles with laboratory testing is very important for both sporadic cases and outbreaks. Testing is used to verify that the infection is measles as well as to help health departments track outbreaks and take measures to limit spread of the disease.
The most common tests for diagnosing acute measles infection include a blood test that measures antibodies (immunoglobulin M, IgM) produced in response to the measles virus and tests for detecting the virus directly either in blood or in a swab from the back of the nose and throat. Only patients with symptoms consistent with measles should be tested. The CDC advises healthcare practitioners who suspect a case of measles to notify their state or local public health officials and to collect both types of samples for testing.
During outbreaks, samples from people suspected of having measles are often sent to public health laboratories for IgM antibody testing or detection of the virus by PCR. If the virus is detected, they can do a genetic test called genotyping, which can be used to determine the genetic makeup of the virus from a particular case or outbreak and help link or unlink cases. Information from genotype testing, performed in public health labs, may help determine where the outbreak might have started and how it spread. (For more details, read the article on Infectious Disease Genetic Testing.)
In one of the most recent outbreaks, health officials were able to identify the individual initially responsible for spreading measles from New York to Michigan (Patient Zero). According to a report in the Washington Post, laboratory tests verified that this individual had measles, and genetic testing confirmed that the strain of measles the individual had matched the viral strain causing the New York City outbreak. Health officials followed-up by contacting the people Patient Zero had visited and tested them for measles. Cooperation between the health officials and community leaders seems to have helped control further spread of measles within the group, according to the report.