Colorado health officials have confirmed the state’s first measles case, adding to outbreaks in 20 other jurisdictions as the United States total surges toward 500 — the largest spike since 2019.

The infected individual worked at the Southwest Deli and Café in Pueblo from March 17 through the 21, Kristin Richmann, a state health department spokesperson, confirmed in an email to The Denver Gazette.

Anyone who at the Deli or locations during this time or at the Southern Colorado Clinic on March 22 should monitor their symptoms for 21 days after exposure and consider avoiding public gatherings, state officials said.

Measles was declared officially eradicated in the U.S. in 2000, with health officials crediting the nation’s vaccination program.

Over the past four decades, cases peaked in 1990, when the U.S. saw 27,808 people infected, according to the Centers for Disease Control and Prevention (CDC). The last major case spike occurred in 2019, when there were 1,274 measles cases over the course of that year.

The unvaccinated individual in Pueblo has been confirmed with measles after traveling to an area in Mexico experiencing an outbreak, according to the Colorado Department of Public Health.

CDC officials maintain that the risk for widespread measles in the U.S. remains low. While a booster is not yet recommended, the CDC is encouraging all Americans be up-to-date on their vaccinations.

For those concerned about waning immunity, Denver Health’s Public Health Institute executive director, Dr. Bob Belknap, said patients can take an antibody test, especially healthcare workers, travelers or those who do not have their vaccination records.

As of March 27, the U.S. had 483 confirmed cases from Alaska and California to Texas, Michigan and New York City.

The number of cases has more than doubled in just two weeks, CDC data shows.

Denver Health officials have been holding standup vaccination clinics for Denver Public Schools’ (DPS) students in the wake of outbreaks, which began in Texas in January.

Most of the infected have been children.

To date, two cases have resulted in deaths.

Measles is a highly contagious disease. Just one individual can infect up to 18 others, making it one of the most contagious viruses known to man, according to the World Health Organization. To put that into context, that means measles is more contagious than COVID-19 (in which one person can infect up to three people with the original strain), polio (up to seven) and chickenpox (up to 12).

The disease transmits particularly easy, as it can linger in the air for hours after a cough or sneeze.

In an outbreak — defined as three or more related cases — one-in five-sickened will require hospitalization and one-in-20 will develop pneumonia.

Measles is a respiratory illness transmitted through direct contact with infected droplets or airborne when a person breathes, coughs or sneezes. Symptoms typically emerge within two weeks of exposure.

A telltale sign of measles is a spotty red rash that starts on the face and spreads to the neck and trunk to the rest of the body. Early onset symptoms include a high fever, cough, runny nose and red, watery eyes. An individual is contagious for about four days before the rash appears and four days after.

In rare cases, measles can cause swelling of the brain and death.

The disease in pregnancy can cause premature births and babies with low birth weights.

To provide “herd immunity” — that’s when enough people in a community have become immune to a disease so it’s harder for that illness to spread — greater than 95% of people need to be vaccinated to prevent measles from spreading, according to health officials.

“It’s certainly the ideal and the goal to get to 95% because the likelihood of a person with measles coming into contact with someone else is less,” Belknap has said.

Those who have received measles, mumps, and rubella (MMR) vaccine or who were born before 1957, when the disease was so widespread everyone exposed to the virus as a child developed natural immunity, are generally considered immune. The CDC recommends that people vaccinated prior to 1968 with an inactivated measles vaccine get another shot.

Health officials consider childhood vaccination as critical for maintaining the health of a community.

With spring break travel, Colorado’s proximity to major outbreaks in Texas and New Mexico and vaccination rates below 95%, health officials have feared the state could face its own outbreak.

“It’s more of a ‘when’ and not ‘if’ we have a case of measles,” Belknap said previously. “All of us are kind of wondering when it’s going to happen, when someone is going to get diagnosed.”

The bulk of the cases nationally have been among either unvaccinated patients or those who have an unknown status.

Before the measles vaccine was developed in the 1960s, an estimated 48,000 Americans were hospitalized and 500 died each year.

According to the latest state health department data, 94% of Colorado students last school year were fully vaccinated against measles, mumps and rubella, all of which are contagious viral diseases that can cause serious health problems.

The measles compliance rate for Denver Public Schools stood at about 92%, as of last month, according to the district. A roughly 3.1-point difference may sound small, but in public health terms, that gap is noteworthy because measles is one of the most contagious diseases in the world.

Vaccination is considered the best way to protect against serious disease, officials said. Vaccination has averted an estimated 60 million deaths between 2000 and 2023, according to the World Health Organization.

“There are no other good recommended measures,” Belknap has said.