Clinical and Geographical Analysis of Rocky Mountain Spotted Fever in Children: Implications for Outbreak Response
Lindsay Ariadna Concha-Mora, Irais Guerrero-Gamiño, Guillermo Andres Negrete-Gómez, Pablo Daniel Treviño-Valdez, José Eduardo Mares-Gil, Oscar Tamez-RiveraAbstract
Background
Rocky Mountain Spotted Fever (RMSF) is a bacterial disease transmitted by infected ticks, with Northern Mexico experiencing a concerning rise in cases, particularly among children. Elevated inflammatory markers, such as C-reactive protein (CRP) and procalcitonin (PCT), indicate an acute inflammatory response but are not specific to RMSF. Monitoring these markers can guide management. A key challenge during the outbreak was delayed diagnosis, highlighting the importance of laboratory test results, clinical data, and georeferencing in outbreak response.
Methods
Clinical geographical data of patients under 16 with confirmed RMSF diagnosed at the Pediatric Reference Hospital (HRMI) in NL, Mexico, from August 2022 to September 2023, were analyzed. HRMI admitted most affected children during the outbreak. A descriptive analysis of clinical and laboratory tests was conducted, and QGIS® was employed to map case distribution, incorporating regional marginalization indices from official sources.
Results
Total of 23 subjects included, with a mean age 8 years (± 3.3). Most (82%) had positive contact with ticks. Time from symptom onset was 4.9 ± 1.8 days. There was high mortality (65.2%) despite in-hospital treatment. Laboratory test results showed CBC: lymphopenia (<2,000/mm3) in 99% of cases, neutrophilia (>8,000/mm3) in 47%, and thrombocytopenia (<150,000/mm3) in 100%. CRP elevation (>0.5 mg/dL) in 100%, hyperferritinemia (>1,000 ng/dL) in 74%, D-dimer elevation (>2,000 mg/dL) in 95%, and hypoalbuminemia (<3.5 g/dL) in 82%. GIS analysis revealed an NNI of 0.54 (z-score -4.1), statistically significant clustered distribution (p < 0.05). Mapping was performed with a KDE ratio of 8755 m, demonstrating two main geographical hotspots for Ped-RMSF. The mean case-to-hospital distance was 24.1 km (± 10.1 km), most cases located in areas with medium (65%) and high (30%) marginalization indices. The majority (95%) of cases lived more than 10 km from HRMI, where diagnosis was made.
Conclusion
The nature of vector-borne diseases necessitates advanced epidemiological surveillance. Using GIS-based analyses, we identified high-burden areas of Ped-RMSF and shared this data with local health authorities to implement effective vector control strategies. Clinical data indicated key points for suspecting and diagnosing RMSF, emphasizing the need for enhanced training for first-care clinicians. Laboratory tests revealed a higher incidence of lymphopenia and thrombocytopenia than previously reported. Elevated inflammatory markers, such as CRP, ferritin, and D-dimer, were common findings, aiding patient management. The clustering pattern of cases demonstrated a non-random distribution, emphasizing the impact of factors like marginalization indices. Our study underscores the importance of GIS in outbreak response strategies.