New cases of measles reported in New York, New Jersey and California bring the total number of infections in the U.S. to at least 671 so far in 2019, the most for a year since the disease was declared eliminated in 2000.

On Wednesday, New York City and suburban Rockland County confirmed an additional 37 measles cases, and California reported seven new cases.

The second-highest number for measles cases in the U.S. was 667 in 2014, according to the Centers for Disease Control and Prevention.

The CDC will report the nation’s official count on Monday and will include updates from at least 22 states.

In New York City and Rockland County, there have been 590 cases since the measles outbreak began in October 2018. Los Angeles reported its first five cases on Monday.

The states that have reported measles cases to the CDC are: Arizona, California, Colorado, Connecticut, Florida, Georgia, Illinois, Indiana, Iowa, Kentucky, Maryland, Massachusetts, Michigan, Missouri, Nevada, New Hampshire, New Jersey, New York, Oregon, Texas, Tennessee and Washington.

Most of the measles cases are unvaccinated children, although some adults may be at risk. In New York, two of the cases have been pregnant women, one of which was diagnosed in mid-April.

Measles during pregnancy can be dangerous for both the pregnant woman and her developing fetus.

"Although the overall risk of birth defects is low, there is a high risk of a miscarriage, stillbirth, prematurity and low birth weight of the baby," NBC News medical correspondent Dr. John Torres said. "For the mother-to-be the risks from developing measles during pregnancy include a much greater chance of pneumonia, hospitalization and death."

Because the measles, mumps and rubella (MMR) vaccine is a live virus, the American College of Obstetricians and Gynecologistsadvise women to be vaccinated before getting pregnant.

As the number of measles cases continue to rise in the U.S., doctors and parents are increasingly concerned about complications and long-term health problems from the respiratory disease.

Ariel Loop of Pasadena, California, worries about her son, Mobius, who was infected with measles when he was 4 months old during the Disneyland outbreak in February 2015. The infant had received other vaccines, but the MMR vaccine is typically given to children around age 1, with a follow-up booster between 4-6 years.

"We did everything I felt like we could've done to keep him safe because he was a preemie," Ariel told NBC News.

After Mobius recovered, Ariel, a nurse, knew to be concerned about long-lasting effects.

“It's not just dangerous in the moment,” Ariel told NBC News, saying that because her child was so young when he got measles, he’s at increased risk of later complications. “it can still kill them 5 to 10 years later. He can still get encephalitis now.”

Another possible complication from measles is the rare but fatal condition called subacute sclerosing panencephalitis or SSPE, which is caused when the measles virus stays in the brain, usually for years, after an infected child has recovered.

"It causes a brain inflammation and a neurologic deterioration," Dr. Steven J. Goldstein, a pediatrician in Brooklyn, told NBC News. "Many of us are very concerned that this SSPE is going to come back because there are so many [cases]."