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CDC issues health advisory on Rocky Mountain spotted fever, 3 die

Rocky Mountain spotted fever is spread to people through bites by wood ticks or dog ticks. In Brazil, it may be spread by the yellow dog tick. Image courtesy of Dr. Christopher Paddock via the Public Health Image Library of the Centers for Disease Control and Prevention.

HQ Team

December 9, 2023: The Centers for Disease Control and Prevention (CDC) has issued a health advisory after three people died following an outbreak of Rocky Mountain spotted fever.

Five patients were identified the fever by the CDC and the California Department of Public Health between July and December 2023.

They had travelled to the city of Tecate in the state of Baja California, Mexico and were admitted to hospitals in southern California.

“Four patients were under the age of 18 years. Three patients were US residents, and two were residents of Mexico. All five patients were hospitalised, and three died,” according to a CDC statement.

Rapidly progressing

Rocky Mountain spotted fever (RMSF) is a severe, rapidly progressive, and often deadly disease transmitted by the bite of infected ticks, although many patients do not recall being bitten by a tick.

The fever is endemic in multiple border states in northern Mexico, “including but not exclusive” to Baja California, Sonora, Chihuahua, Coahuila, and Nuevo León.

In these regions, the pathogen (Rickettsia rickettsii) can be transmitted by brown dog ticks (Rhipicephalus sanguineus) which are closely associated with domestic dogs in urban and peri-urban environments.

In the Baja California region — Mexicali, Tijuana, Ensenada, and Vicente Guerrero— there were 88 confirmed RMSF cases in 2022 with an incidence of 2.3/100,000 population.

Of the 88 confirmed cases, there were 36 deaths. In contrast, one to three cases of RMSF are reported among San Diego County residents annually.

Coma, cerebral oedema

 Additional non-resident cases are also diagnosed in the country and are not included in the case count.  

In 2022 there was one confirmed and one probable case among the county residents with an additional two probable cases among nonresidents. There were no deaths among San Diego County resident cases reported last year.  

RMSF signs and symptoms can be relatively mild and non-specific during the first four days of illness and include a low-moderate fever, headache, gastrointestinal symptoms, abdominal pain, myalgia, rash, and oedema around the eyes and on the back of hands. 

Patients with more advanced disease, generally on or after five days of illness, may develop altered mental status, coma, cerebral oedema, respiratory compromise, necrosis, and multi-organ system damage.


The disease is rapidly progressive, and half of all people who die from this disease succumb within eight days of illness onset. Untreated disease is often fatal, and the case fatality rate of RMSF in Mexico can exceed 40%.

RMSF is a multi-system disease and can also involve the lungs, heart, kidneys, and central nervous system.

Doxycycline is the treatment of choice for patients of all ages. Early treatment with doxycycline saves lives, according to the CDC.

A CDC advisory provides information about a public health incident. A health alert conveys the highest level of importance about a public health incident.

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