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. 2021 Jan;104(1):190-197.
doi: 10.4269/ajtmh.20-0854.

Epidemiology and Clinical Features of Rocky Mountain Spotted Fever from Enhanced Surveillance, Sonora, Mexico: 2015-2018

Diego I Álvarez-López  1 , Estefanía Ochoa-Mora  1 , Kristen Nichols Heitman  2 , Alison M Binder  2 , Gerardo Álvarez-Hernández  1 , Paige A Armstrong  2
Affiliations

Epidemiology and Clinical Features of Rocky Mountain Spotted Fever from Enhanced Surveillance, Sonora, Mexico: 2015-2018

Diego I Álvarez-López et al. Am J Trop Med Hyg. 2021 Jan.

Abstract

Rocky Mountain spotted fever (RMSF), caused by Rickettsia rickettsii, is a severe and potentially fatal tick-borne disease. In 2015, Mexico issued a declaration of epidemiologic emergency in response to ongoing outbreaks of RMSF in northern Mexico. Sonora state is one of the most heavily impacted states in Mexico, with historic case fatality rates (CFRs) of 18%. We summarized data from enhanced surveillance to understand demographic, clinical, and treatment factors associated with the high mortality. We conducted a retrospective review of confirmed and probable RMSF cases reported to the General Directorate of Health Promotion and Disease Prevention in Sonora. A case of RMSF is defined as fever (> 38.5°C), plus two symptoms, and epidemiologic criteria. A confirmed case requires laboratory evidence. During 2015-2018, a total of 510 cases of RMSF were reported; 252 (49%) were in persons aged ≤ 18 years. Case fatality rate was 44% (n = 222). Older age and being confirmed by PCR were associated with fatal outcome (P-value < 0.01). The mean time from onset of symptoms to treatment with doxycycline was 7.9 days (SD ± 5.5). Hot spot analysis revealed neither areas of inordinately high nor low incidence, rather clusters of disease in population centers. The CFR for RMSF in Sonora remains high, and a large proportion of cases are seen in persons aged ≤ 18 years. Whereas previously children experienced a disproportionately high CFR, interventions have reversed this trend. Disease clusters in urban nuclei, but location remains a predictor of fatal outcome.

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Conflict of interest statement

Disclaimer: The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the Centers for Disease Control and Prevention.

Figures

Figure 1.
Figure 1.
Reported cases of Rocky Mountain spotted fever and case fatality rates (CFRs) by year—Sonora, Mexico, 2015–2018. This figure appears in color at www.ajtmh.org.
Figure 2.
Figure 2.
Cases of Rocky Mountain spotted fever by month of illness onset and corresponding case fatality rate by month—Sonora, Mexico, 2015–2018. This figure appears in color at www.ajtmh.org.
Figure 3.
Figure 3.
Proportion of fatal and nonfatal cases of Rocky Mountain spotted fever in Sonora, Mexico, 2015–2018, among all cases (Map A) and persons aged < 18 years (Map B).
See this image and copyright information in PMC

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