Measles Cases Continue to Rise in the US

Measles is caused by the measles virus, a single-stranded, negative-sense, enveloped RNA virus of the genus Morbillivirus within the family Paramyxoviridae. Measles is a highly contagious, vaccine-preventable infectious disease. 

For most countries, the recommendation is that children be immunized against measles at 12 months, generally as part of a three-part MMR vaccine (measles, mumps, and rubella). Waiting to vaccinate an infant until 12 months of age is necessary to ensure the immune system can adequately respond to the vaccine to produce immunity. Further, children between the ages of four and five are given a second dose of the vaccine to increase rates of immunity.

US measles outbreak

According to the U.S. Centers for Disease Control and Prevention (CDC), as of March 21, 2024, a total of 64 measles cases were reported by 17 jurisdictions: Arizona, California, Florida, Georgia, Illinois, Indiana, Louisiana, Maryland, Michigan, Minnesota, Missouri, New Jersey, New York City, Ohio, Pennsylvania, Virginia, and Washington. 

Measles was declared eliminated from the US in 2000, which means the disease is no longer constantly present in the country. However, if a measles outbreak continues for a year or more, the US could lose its measles elimination status. Healthcare officials should be aware of possible measles cases.

Measles cases usually occur when unvaccinated or under vaccinated citizens from the US travel abroad and then transmit the infection (disease) to other individuals who are not vaccinated or have no immunity to measles. During this most recent outbreak over the past several weeks, the increased number of imported measles cases is mirroring the rise in global cases of measles and the growing global threat from this dangerous pathogen. 

Due to these ongoing public health concerns, the CDC has asked people who intend to travel internationally to ensure  they are protected against measles. The best way to protect yourself and others from measles is via vaccination. You should plan to be fully vaccinated at least two weeks prior to your departure. However, even if your trip is less than two weeks away and you’re not protected against measles, you should still get a dose of the measles-mumps-rubella (MMR) vaccine. 

Measles transmission

Measles is an airborne disease that spreads easily from one person to the next through the coughs and sneezes of infected people. The virus lives in the nose and throat mucus of an infected person, so it is perfectly positioned to spread to others via coughing and sneezing. If other people breathe the contaminated air or touch an infected surface then touch their eyes, noses, or mouths, they can become infected. 

According to the CDC, measles is so contagious that if one person has it, up to 90 percent of the people close to them who are not immune will also become infected. Anyone who is infected with this virus can spread measles to others from four days before to four days after the typical rash appears. A dangerous pathogen, measles can remain viable for up to two hours in an airspace after an infected person leaves an area.

Humans are the sole reservoir of the measles virus; animals do not get or spread measles. This important characteristic makes it feasible to eradicate measles via vaccination. 

Signs and symptoms of measles

Symptoms from an infection usually appear 7 to 14 days after virus contact and usually include high fever, cough, runny nose, and watery eyes. Measles rash appears 3 to 5 days after the first symptoms. This isn’t a typical rash, and it can be dangerous, especially for babies and young children. Classic symptoms include a four-day fever (“the 4 Ds”) and the “3 Cs”—cough, coryza (head cold, fever, and sneezing), and conjunctivitis (red eyes)—along with a maculopapular rash. 

Koplik spots, which appear as tiny white spots, may appear inside the mouth two to three days after symptoms begin. Then, three to five days after symptoms begin, a rash breaks out. The rash usually begins on the face as flat red spots near the hairline that then spread downward to the neck, trunk, arms, legs, and feet. One may see small, raised bumps on top of the flat red spots, and the spots may coalesce as they spread. Finally, one’s fever can spike to 104° Fahrenheit with the rash appearing.

Measles can lead to severe complications and hospitalization. Children younger than 5 years of age and adults older than 20 years of age are more likely to suffer from complications.

Measles testing

While measles can be diagnosed based on the typical signs and symptoms, especially with the observation of Koplik's spots, the CDC and other experts strongly recommend laboratory confirmation. 

A nasopharyngeal swab, throat swab, or urine specimen, as well as a blood specimen, should be collected from all patients with clinical features indicative of measles. Nasopharyngeal or throat swabs are preferred over urine specimens. 

Laboratory diagnosis of measles can be done with confirmation of positive measles IgM antibodies or detection of measles virus RNA from throat, nasal, or urine specimen via reverse transcription polymerase chain reaction (RT-PCR) assay. RT-PCR is particularly useful to confirm inconclusive IgM antibody results. 

Saliva can also be utilized for salivary measles-specific IgA testing, which is sometimes useful for those who can’t have blood drawn. The saliva-based IgA method is not a preferred method, as saliva contains many other fluids and proteins that may make it difficult to collect samples and detect measles antibodies. Saliva also contains 800 times fewer antibodies than blood samples do, which makes salivary testing additionally difficult. A patient history that shows positive contact with other people known to have measles adds evidence to the diagnosis.

Regions or areas with low prevalence due to high vaccine uptake can present challenges. For example, routine serological methods such as IgM detection may have a reduced positive predictive value and require confirmation by other methods. Direct detection via viral culture (less common) or of viral genomic material using RT-PCR methodologies can play an important role for laboratory confirmation of acute infections. Importantly, genotyping viruses can provide useful molecular epidemiological data for differentiating vaccine from wild-type strains, linking cases and outbreaks, and tracking geographic spread and elimination.

Complacency kills

In the US, since around 1950, vaccination for measles was rarely questioned in the public health community. In fact, many of today’s clinicians have never seen or experienced the potential danger of measles firsthand. We have all become complacent to the diabolical nature of pathogens because of our past success at reducing them or eliminating them—will we continue to ignore the warning signs? Even if we don’t see them in our daily lives, pathogens are always present, incubating in an unknown reservoir (animal, plant, or environment) and waiting to emerge or reemerge and remind us of lessons passed.