A woman in Washington state is the first person to die of measles in the United States in a dozen years, authorities said today. But the disease was discovered only after the woman's death — how did doctors miss her diagnosis? 

The woman appears to have caught measles when she stayed at local medical facility. She had several other health conditions and was taking medications that suppressed her immune system, according to a statement from the Washington State Department of Health. She died of pneumonia this spring, and it was during her autopsy that doctors determined that her pneumonia was due to measles.

The woman was missing some of the classic symptoms of measles; for example, she didn't develop a rash, the statement said.

It's not clear exactly why doctors failed to catch her measles diagnosis until after her death, but the woman's compromised immune system may have played a role, said Dr. Amesh Adalja, an infectious-disease specialist and a senior associate at the University of Pittsburgh Medical Center's Center for Health Security. [7 Devastating Infectious Diseases]

People with compromised immune systems are more susceptible to infections. There are a number of more common infectious that doctors would suspect before they would think of measles, especially because the woman did not have textbook symptoms of measles, said Adalja, who was not involved in the woman's case.

"In today's world, where measles is still a fairly rare occurrence, [doctors] would be thinking of the usual suspects, not necessarily measles," Adalja told Live Science. "If she didn't have a very prominent rash, measles wouldn't be high up on anyone's list" of possible diagnoses. Some common causes of pneumonia are the flu, pneumococcus or respiratory syncytial virus, according to the Centers for Disease Control and Prevention.

In addition, because a person's immune system plays a role in the type of symptoms he or she experiences, a person who is immunosuppressed can show different symptoms of measles than a typical person would, Adalja said. The woman's compromised immune system could explain why she had measles but not its characteristic rash, he said.

Finally, many doctors today haven't seen a case of measles, so they are less familiar with the disease, particularly in adults, Adalja said.

The woman's atypical measles symptoms, along with the tendency for doctors to have not seen measles before, is almost "a recipe for missing a diagnosis," Adalja said.

Officials from Washington State Department of Health said that the "tragic situation illustrates the importance of immunizing as many people as possible to provide a high level of community protection against measles." 

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