CDC issues health alert for deadly tick-borne disease

The Centers for Disease Control and Prevention on Friday warned clinicians and the public about an outbreak of a rare but deadly tick-borne disease that hospitalized five patients in Southern California, killing three of them, after they traveled to or lived in a Mexican border city in recent months.

Rocky Mountain spotted fever (RMSF) is transmitted by the bite of infected ticks that live primarily on dogs. It’s rare in the United States but it has emerged at epidemic levels in northern Mexico, where more than 2,000 cases, resulting in hundreds of deaths, have been reported in the past five years.

In a health advisory issued late Friday, the CDC said the five patients had been diagnosed since late July. All had traveled to or lived in the city of Tecate, in the northern Mexican state of Baja California, within two weeks of getting sick. All five sought care in hospitals in Southern California, including four pediatric patients. CDC officials declined to provide more details about the individuals, to protect their privacy. Three of the patients were U.S. residents, and two were siblings who lived in Mexico. Two deaths were pediatric patients and one was an adult.

The cases occurred between late July and late October.

Christopher Paddock, a CDC chief medical officer and expert on the disease, said the health agency wants to alert clinicians in cities and towns near the U.S.-Mexico border to raise awareness during the holiday season, when many people who live in Southern California and in northern Mexico may be traveling to visit family and friends. The agency also issued a health travel alert about the outbreak, noting that RMSF has been found in urban areas of several parts of northern Mexico.

RMSF is endemic in multiple border states in northern Mexico, including Baja California, Sonora, Chihuahua, Coahuila and Nuevo León, and areas of the southwestern United States.

“This disease is extraordinarily unfortunate because half of the patients die in the first eight days of illness,” Paddock said. RMSF can be treated if the diagnosis is made quickly. But its early symptoms - low fever, headache, gastrointestinal discomfort - resemble those of many illnesses, so the disease is often not diagnosed in time to be treated, Mexican and U.S. health officials said.

In any given year in the United States, cases of Rocky Mountain spotted fever are rare and sporadic. “What was unusual here, we’re talking five cases over the span of just a few months,” Paddock said.

Rocky Mountain spotted fever requires therapy with limited antibiotics, typically doxycycline. But that antibiotic is not a drug that doctors typically use as a first-line treatment, because clinicians may suspect other more common bacterial infections for which other antibiotics are more effective.

Untreated, RMSF is often fatal. The case fatality rate of RMSF in Mexico can exceed 40%, according to the CDC. Children under 10 are five times as likely as adults to die of the disease, which affects multiple organs, including the lungs, heart, kidneys and central nervous system.

Most patients present for care in the first few days of illness, and if a clinician does not consider RMSF as a possible diagnosis, patients will continue to get sicker. After Day 5 or 6, “even if the therapy is started, not all patients can be rescued and will have such severe disease that they will go and die,” Paddock said.

The ecology of Rocky Mountain spotted fever is also quite different from what clinicians typically think of as areas for tick-borne diseases. In the United States, clinicians tend to associate tick-borne diseases such as Lyme disease with outdoor activity, such as hiking in the woods, Paddock said.

But RMSF has been spreading in urban and heavily populated regions in northern Mexico. CDC and state health officials became aware of one patient who died at the end of October, but it wasn’t until after the patient died that officials realized the patient had traveled to Tecate. By then, officials at California’s health department had learned of additional confirmed cases in Southern California. Retrospective investigations led CDC and state health officials to realize the common exposure in all five cases was Tecate.