Study warns of increasing Rocky Mountain spotted fever cases among children in California

By Dr. Sushama R. Chaphalkar, PhD.Reviewed by Lily Ramsey, LLMOct 15 2024

Cutting-edge diagnostic method identifies severe cases of Rocky Mountain spotted fever in California children, highlighting the need for increased awareness and early treatment to prevent fatalities.

Study: Rocky Mountain Spotted Fever in Children along the US‒Mexico Border, 2017–2023. Image Credit: David Jara Bogunya/Shutterstock.com

A recent study published in Emerging Infectious Diseases reported seven cases of children hospitalized with Rocky Mountain spotted fever (RMSF), a potentially fatal disease, at a center in California.

In all cases, the deoxyribonucleic acid (DNA) of the causative pathogen, Rickettsia rickettsii, was detected using plasma microbial cell-free next-generation sequencing (mcf-NGS). This highlights the potential of mcf-NGS as an effective method for early diagnosis of RMSF, even in patients who had not recently traveled to endemic areas.

Background

Rocky Mountain spotted fever (RMSF) is a severe tick-borne infection with a case-fatality rate of 7–10% in the US, rising to over 50% in some border states. Diagnosing RMSF is challenging and requires a high level of clinical suspicion, as the pathogen is rarely isolated through standard methods, and nearly half of patients report no history of a tick bite.

Symptoms often overlap with other diseases, making diagnosis even more difficult in nonendemic regions. Common diagnostic methods include serologic testing, polymerase chain reaction (PCR), and specialized cultures. Indirect immunofluorescence antibody assays are frequently used, though it may take over a week for antibodies to develop.

Although historically rare in California, RMSF has become endemic in northern Mexico, with a significant rise in cases since 2008, particularly among children. Recent reports detailed five severe RMSF cases in southern California linked to travel to Tecate, Mexico, with four cases resulting in death, underscoring the need for increased awareness and prompt treatment. This study examines seven additional RMSF cases in children from San Diego.

About the study

A retrospective chart review was conducted with seven children diagnosed with RMSF who were hospitalized at a center in San Diego between January 2017 and August 2023. The mean age of the patients was 7.3 years. Data were obtained from electronic medical records, and mcf-NGS-based testing was performed at the discretion of the treating infectious disease physicians.

RMSF cases were confirmed through serology or PCR testing, with additional verification against reports from the San Diego County Health and Human Services Agency. Notably, there were no pediatric RMSF cases in San Diego where mcf-NGS was not conducted, nor were there any instances where mcf-NGS results were negative while other tests confirmed RMSF.

Results and discussion

R. rickettsii was detected through mcf-NGS in all the cases. Six children were critically ill and were admitted to the pediatric intensive care unit. The median duration of symptoms before hospital admission was six days, and the median turnaround time for mcf-NGS results was 3.3 days. Antimicrobial therapy was adjusted based on mcf-NGS findings in four of the seven cases.

Case 1

A five-year-old boy from Tecate, Mexico, presented with fever, vomiting, abdominal pain, rash, and altered mental status after a tick bite. Punctate foci of cytotoxic edema were seen in the brain, indicative of small vessel vasculitis. He was treated with doxycycline for 19 days and survived but had persistent deficits in motor function and speech.

Case 2

A 10-year-old girl with rash, fever, and conjunctival injection had a rash that spread to her palms and soles. After hospitalization for hypotension and altered mental status, she was treated with doxycycline. She made a complete recovery.

Case 3

A seven-year-old boy experienced fever, rash, and joint pain but had no known tick exposure. After six days in the hospital without empirical therapy, mcf-NGS detected R. rickettsii. He was started on doxycycline, leading to symptom resolution. He was given doxycycline for a week, and he returned to baseline health.

Case 4

A 14-year-old girl from rural Mexico developed a generalized rash and altered mental status after a presumed insect bite. Cerebrospinal fluid showed elevated protein and pleocytosis. She received doxycycline for 14 days but was transferred to another hospital with significant motor and speech deficits.

Case 5

A 10-year-old girl from El Centro had a fever, abdominal pain, and rash after potential tick exposure. She was treated with doxycycline and ceftriaxone, with serology confirming the diagnosis later. She completed treatment and was discharged in good health without neurological sequelae.

Case 6

A 17-month-old boy from Tecate, Mexico, presented with fever, lethargy, rash, and seizures. MRI showed brain infarcts from vasculitis. He was treated with doxycycline and other antibiotics and discharged with better mental status and no focal deficits.

Case 7

A 4-year-old boy from Alpine presented with fever, hypotension, abdominal pain, and rash, initially treated for an ear infection. He was admitted with worsening symptoms and received broad-spectrum antibiotics. R. rickettsii was later detected, but he was discharged at baseline health after ten days of doxycycline and additional antibiotics.

Conclusion

In conclusion, despite the small sample size and retrospective design of the present study, the findings indicate that plasma mcf-NGS could enhance diagnostics in cases where standard isolation methods fail or when clinical presentations are atypical.

This is particularly relevant in non-endemic regions. The researchers emphasize the need for monitoring RMSF epidemiologic trends and the importance of early detection and treatment to prevent severe illness and improve outcomes.