Articles from Emerging Infectious Diseases

Western equine encephalitis virus (WEEV) reemerged in Argentina during 2023–2024, raising public health concerns and posing a potential threat to blood transfusion safety. We assessed the effect of WEEV circulation on the blood supply by implementing responsive, community-informed interventions within a regional hemovigilance system, including epidemiologic mapping, enhanced donor selection criteria, and alphavirus-specific nucleic acid testing. Among 637 donors residing in outbreak-affected areas, we detected 1 asymptomatic viremic donor. Phylogenetic analysis showed that the viral sequence clustered within the contemporary South American outbreak lineage, consistent with ongoing regional transmission. Those findings demonstrate silent WEEV circulation among blood donors and highlight the critical role of donor surveillance as a sentinel system for emerging arboviruses. Hemovigilance provides valuable insights into viral circulation in the broader population, underscoring the need to integrate molecular surveillance into routine blood bank practices to strengthen transfusion safety and public health preparedness.

Existing methods to identify patients infected with Salmonella enterica serovar Typhi or Paratyphi are not adequately accurate, affordable, or efficient. We evaluated the performance of antibodies to Salmonella Typhi hemolysin E (HlyE) and lipopolysaccharide (LPS) in Bangladesh, Nepal, and Pakistan for enteric fever case identification. We measured plasma concentrations of HlyE and LPS IgA in blood culture–confirmed enteric fever case-patients and in febrile controls with laboratory-confirmed alternative etiologies. Combining LPS and HlyE IgA discriminated enteric fever cases from other febrile illnesses with an area under the receiver operating characteristic curve (AUC) of 0.93 (specificity 86% at a fixed 90% sensitivity). LPS IgA alone performed nearly as well (AUC 0.92). In children <5 years of age, the combined biomarkers outperformed either biomarker alone (AUC 0.96 vs. 0.94 for HlyE, 0.93 for LPS). Our findings support use of HlyE and LPS IgA–based assays for enteric fever diagnosis in endemic settings.

Dog importation into Canada has grown substantially since the early 2010s, and concerns have been raised regarding the potential introduction of infectious agents. We conducted a qualitative risk assessment of infectious agents associated with canine importation into Canada. We adapted international risk assessment methodologies coupled with an expert consultation. We estimated likelihood of entry, likelihood of canine exposure, and magnitude of impact of exposure to individual canines and the canine population for all hazards (n = 53). We also completed estimates for likelihood of human exposure and magnitude of impact of exposure on individual humans and the human population for zoonotic hazards (n = 33). Hazards were commonly ranked moderate or high for likelihood of entry and exposure estimates. Magnitude of impact of exposure estimates were assessed at much lower levels, indicating more restricted health impacts. Our study provides a foundation for future risk mitigation, including caregiver education, veterinary assessments, and importation regulations.

Highly pathogenic avian influenza clade 2.3.4.4b virus continues to circulate in North America and has caused severe human disease. That clade includes genotype D1.1, which became dominant in birds in late 2024. Recent phylodynamic reconstructions place D1.1 emergence in mid-2024 but differ on its inferred origin and early dissemination pathways. We combined targeted surveillance of wild birds in Arizona with publicly available US clade 2.3.4.4b hemagglutinin sequences to estimate when D1.1 genotype emerged and to infer its diffusion among the 4 major US flyways. Phylodynamic analyses showed transitions concentrated among adjacent flyways regions, consistent with stepwise dissemination during fall 2024 and limited support for long-distance Pacific–Atlantic exchange. The Pacific Flyway showed patterns consistent with an early source and the Central Flyway with a secondary hub linked to onward spread. Our findings support coordinated genomic surveillance across adjacent flyways to reduce detection delays and improve situational awareness during rapid viral expansion.

Melioidosis, caused by Burkholderia pseudomallei, is an emerging disease in the United States and was declared endemic to the Gulf Coast region in 2022. Melioidosis has been sporadically reported in the American continents, the Caribbean, and more recently in Africa. We conducted lethal dose analyses in BALB/c and C57BL/6 mice exposed to small particle aerosols of B. pseudomallei strains from the Western Hemisphere and Africa. Those isolates exhibit a variety of virulence patterns, including rapidly-lethal disease and delayed onset of fatal disease. We found that the isolates we tested grew similarly in culture but displayed major differences in biofilm formation. Our data contribute to the growing knowledge of geographically distinct B. pseudomallei isolates and aid in ensuring that medical countermeasures in development are effective against a diverse collection of bacterial strains.

Highly pathogenic avian influenza H5NX clade 2.3.4.4b viruses continue to circulate globally. Reintroduction of Eurasian lineage viruses into North America and reassortment with endemic low pathogenicity strains have resulted in new genotypes, including D1.2. To assess pathogenicity and cellular tropism, we intranasally inoculated genotype D1.2 virus into pigs. We isolated virus from nasal secretions from most inoculated animals for multiple days. At 5 days postinoculation, PCR and immunohistochemistry detected virus in musculoskeletal, respiratory, digestive, lymphatic, and nervous systems, and virus was isolated from meat juice. At 35 days postinoculation, we detected viral antigen and low levels of RNA in the brain of an animal with lesions consistent with a viral etiology and found viral antigen in the ethmoid of 2 animals. Consistent detection in nasal swab specimens, combined with subclinical respiratory infection, suggest that identifying infection in commercial swine without overt respiratory signs could be difficult.

During November 2023–April 2024, a total of 1,543 horses with neurologic disease from rural areas in 17 provinces of Argentina were reported to national animal health authorities. Nested reverse transcription PCR, quantitative real-time reverse transcription PCR, and sequencing of equine brain necropsies confirmed western equine encephalitis virus (WEEV) infection in 23 horses and 1 sheep. Phylogenetic analyses identified a lineage previously detected in Argentina in 1957, overlapping areas affected during the 1980s epizootics. Overall, we aspirated 1,362 female mosquitoes (12 species) from 1 of the most affected areas; Aedes (Ochlerotatus) albifasciatus (70.1%) and Ae. (Ochlerotatus) scapularis (26.8%) mosquitoes were the most abundant species. Three of 27 mosquito pools (n = 1,089 mosquitoes) were identified as WEEV positive (2 Ae. albifasciatus, 1 Ae. scapularis). Increased rainfall, agricultural expansion, vector proliferation, and low vaccination coverage were likely key factors contributing to the reemergence of WEEV.

Persons with occupational exposure to swine might be at disproportionate risk for zoonotic swine influenza A virus. To evaluate human antibody responses, we tested serum or plasma from swine veterinarian, farm employee, and general population cohorts by hemagglutination inhibition assays against representative swine and human seasonal influenza vaccine strains. We analyzed hemagglutination inhibition data by antigenic cartography to assess strain relationships and reproduction number modeling to evaluate pandemic potential using age-stratified immunity profiles. Occupationally exposed groups had lower human seasonal vaccine uptake (45.5% vs. 70%) and lower odds of seropositivity to several H1 and H3 strains from swine than did general population cohorts. One swine strain exhibited significant antigenic drift (3.62 antigenic units) from its nearest vaccine strain. Multiple strains required lower reproduction number thresholds for pandemic spread (1.09–1.35) than recorded pandemic strains (1.46–1.80), demonstrating that population immunity gaps heighten zoonotic risk to circulating swine H1 and H3 strains.

Chronic obesity is a growing public health threat in the United States; >40% of adults are affected. We retrospectively assessed the frequency of medically attended infection in infants born during 2008–2012 relative to absolute weight and body mass index outcomes at age 4–6 years of age and 10–15 years of age. Multivariable regression revealed those with early clinical infection had higher rates of obesity at 4–6 years and 10–15 years than those without, proportional to the number of infections diagnosed and corresponding to significant weight increases. Compared with infants whose infections were not treated with antimicrobial drugs, treatment was less predictive of weight outcomes. Most infections were viral. Our investigation found a correlation between infections diagnosed in infancy and later weight outcomes, but we could not determine the cause.

After the 2023 Equatorial Guinea Marburg virus (MARV) outbreak, surveillance of 181 persons in southern Cameroon detected MARV antibodies in 3 persons and Ebola virus antibodies in 7. Testing of 289 captured bats, including 158 Rousettus aegyptiacus bats, did not detect MARV RNA. Enhanced surveillance for regional filovirus spillover risks is warranted.

We performed a 1-year mosquito survey in Dubai, United Arab Emirates, after a dengue virus outbreak in 2024. We collected 1,598 Aedes aegypti mosquitoes and detected dengue virus in 5 pools of <20 mosquitoes. Our findings underscore the importance of sustained vector surveillance for dengue virus in arid urban environments.

We identified human Borrelia miyamotoi infections in Slovenia in 2 of 337 adults with undifferentiated fever tested positive by metagenomic sequencing and PCR. Both patients reported recent local tick bites. The illness was mild and self-limited. Our findings underscore the need to consider this pathogen in evaluating fever after tick bite.

In February 2025, we detected highly pathogenic avian influenza virus A(H5N1) clade 2.3.4.4b virus in a fetal bovine serum lot during routine adventitious agent testing. Sequencing confirmed H5N1 genotype B3.13 virus. We found low viral loads in additional samples from the same lot. Heating at 56°C for 30 minutes completely inactivated the virus.

Twenty-four patients in the Netherlands who became ill during November 2024–February 2025 were part of a hepatitis A virus genotype IA cluster. Consumption data combined with detection of RNA of the hepatitis A outbreak strain in a food product pointed toward frozen blueberries from a specific supermarket chain as the source.

An outbreak of Salmonella enterica serovar Reading in Sydney, New South Wales, Australia, was linked to a restaurant and meat products purchased from South Asian grocery stores. Salmonella Reading was isolated from dried bovine meat products obtained from the restaurant and traced to an unlicensed meat processor and manufacturer of dried meat products.

Norovirus incidence increased in England during 2022–2025, when GII.17 replaced GII.4 as the dominant genotype. By using nationally linked norovirus testing and fatality data, we found age and care setting, but not genotype, were associated with case-fatality risk. Increased incidence might reflect changes in transmissibility or population immunity.

We describe congenital syphilis in a newborn whose mother had secondary syphilis diagnosed during pregnancy and received a single penicillin dose. Molecular methods detected an extremely low Treponema pallidum load in the mother but higher load in the neonate. Our findings support using molecular methods for detecting vertical T. pallidum transmission.

We report the Trans-Pacific expansion of Vibrio parahaemolyticus pandemic clone sequence type 36 and emergence of sequence type 50 in Oceania, causing seafoodborne outbreaks in New Zealand. Unusual features of the outbreaks included diversity of the seafood sources and pathogenic strains and timing, occurring in both winter and summer seasons.

We report 6 cases of camel prion disease in dromedaries in Tunisia, confirming widespread occurrence of the disease in North Africa. Affected animals showed neurologic signs and disease-associated prion protein accumulation in brain and lymphoid tissues. These findings highlight the importance of active surveillance and investigation of the epidemiology, transmission, and public health implications of this disease.

Public health measures during COVID-19 were associated with reduced respiratory syncytial virus cases in Hong Kong, China. Mask wearing was associated with a 35% reduction; avoidance behaviors and hand hygiene were also associated with reductions. After the mask mandate was lifted in March 2023, we observed resurgence in RSV activity.

We investigated an outbreak of 5 hepatitis A cases among skilled nursing facility residents in Los Angeles County, California, USA, including 3 who were vaccinated after exposure. Our results suggest that persons in congregate living facilities should receive both the vaccine and immune globulin after hepatitis A exposure to mitigate further transmission.

Banked serum samples from ferrets previously immunized with the Ebola virus vaccine revealed a prominent but limited humoral immune response that cross-reacted with Bundibugyo virus. The supporting immunogenicity data we report may help guide the ongoing response to the current outbreak of Bundibugyo virus in the Democratic Republic of the Congo.

Lactococcus garvieae bloodstream infection in a woman in Germany resulted in spondylodiscitis and bioprosthetic mitral valve endocarditis. Six weeks of ceftriaxone followed by 10 days of doxycycline led to sustained clinical and microbiological resolution. This case highlights the need for thorough diagnostic testing and individualized, shared decision-making in infective endocarditis cases.

We report the temporal and geographic distribution of ticks and tickborne Borrelia, Ehrlichia, and Rickettsia spp. bacteria in Texas, USA, 2014–2021, updating the previous 2008–2014 passive surveillance report. We identified 9 tick species and an overall prevalence of tested bacterial species of 26.0%, predominantly Rickettsia amblyommatis.

We analyzed antimicrobial resistance markers in 189 Neisseria gonorrhoeae patient encounters from 2 US military medical centers. Co-occurring resistance-associated markers were common; we detected plasmid-mediated β-lactamase in extragenital sites. Our findings highlight the importance of anatomic site–specific surveillance and, potentially, molecular antimicrobial resistance detection to guide screening and treatment strategies.

We analyzed 2015–2024 national surveillance data on Kudoa septempunctata parasite–associated foodborne disease in South Korea. Monthly cases decreased 95% during the COVID-19 pandemic, with no significant recovery through 2024; affected municipalities dropped from 89 to 27. Our findings are consistent with restaurant-based raw fish consumption as the principal transmission pathway.

We report an outbreak of infections with a novel protoparvovirus on several commercial farms in the Netherlands and associations with a clinical syndrome in pigs characterized by exophthalmos and erythema. Evidence of involvement of this virus, highly similar to a vulpine parvovirus, was substantiated by long-read sequencing and in situ hybridization techniques.

We report detection of a bla_OXA-23-positive Proteus mirabilis clinical isolate through Antimicrobial Resistance Laboratory Network testing that is closely related to OXA-23 producers identified in Europe. Combined with similar reports internationally, this finding suggests that Enterobacterales might serve as a silent reservoir of carbapenemase genes commonly associated with Acinetobacter species.

A patient recounts her experience of surviving zoonotic endocarditis caused by the rare bacterial pathogen Lactococcus garvieae. She reflects on the potentially life-changing medical decisions she faced and the physical and emotional challenges of recovery. Her story highlights resilience, adaptation, and the gradual journey back to everyday normality.

Western equine encephalitis virus (WEEV) reemerged in Argentina during 2023–2024, raising public health concerns and posing a potential threat to blood transfusion safety. We assessed the effect of WEEV circulation on the blood supply by implementing responsive, community-informed interventions within a regional hemovigilance system, including epidemiologic mapping, enhanced donor selection criteria, and alphavirus-specific nucleic acid testing. Among 637 donors residing in outbreak-affected areas, we detected 1 asymptomatic viremic donor. Phylogenetic analysis showed that the viral sequence clustered within the contemporary South American outbreak lineage, consistent with ongoing regional transmission. Those findings demonstrate silent WEEV circulation among blood donors and highlight the critical role of donor surveillance as a sentinel system for emerging arboviruses. Hemovigilance provides valuable insights into viral circulation in the broader population, underscoring the need to integrate molecular surveillance into routine blood bank practices to strengthen transfusion safety and public health preparedness.

Trichinella spp. nematodes are parasites that can cause trichinellosis in humans after consumption of infected, undercooked meat. A November 2024 trichinellosis outbreak in western North Carolina, USA, resulted in 3 cases (2 probable, 1 confirmed), all linked to undercooked bear jerky. In total, 6 persons consumed the implicated meat (attack rate 50%). Molecular testing identified Trichinella spiralis in leftover meat from the same bear. This outbreak provides evidence of changing trichinellosis patterns. Low-cost safety measures and prevention efforts regarding safe wild game preparation are needed to avoid future outbreaks.

Anaplasmosis, an emerging tickborne zoonosis, infrequently involves the central nervous system, and cerebrospinal fluid (CSF) profiles of anaplasmosis remain poorly characterized. We conducted a multisite retrospective study of patients hospitalized with anaplasmosis during November 1, 2014–November 29, 2024, in Minnesota and Wisconsin, USA, a hyperendemic region. Included patients had anaplasmosis confirmed by PCR on blood samples, exhibited neurologic symptoms, and had lumbar puncture procedures. Ten hospitalized patients met inclusion criteria, 6 with meningitis, 3 with meningoencephalitis, and 1 with encephalitis. CSF findings were within reference ranges for 5 patients; 4 patients demonstrated mild lymphocytic pleocytosis, but glucose and protein levels were within reference ranges. One patient underwent a traumatic lumbar puncture resulting in neutrophilic pleocytosis. CSF abnormalities did not correlate with neurologic severity, suggesting a cytokine-mediated process rather than direct central nervous system infection. All patients rapidly improved with doxycycline, highlighting the need for early recognition and empiric therapy for anaplasmosis.

Diagnosis of coccidioidomycosis is challenging and requires a high index of clinical suspicion. We estimated the incidence and duration of, and risk factors associated with, diagnostic delays and missed opportunities in the diagnosis of coccidioidomycosis. We conducted a retrospective analysis of health insurance claims data in the United States during 2001–2022 included in the Merative MarketScan Databases. Using a case-crossover design and a bootstrapping approach, we estimated the number of excess visits for coccidioidomycosis-related symptoms before diagnosis. We also evaluated potential factors associated with delay. We estimated that almost 60% of patients experienced >1 missed opportunity for diagnosis; the average diagnostic delay was 29.69 (95% CI 28.25–31.18) days. Missed opportunities were predominantly observed in outpatient settings (73%) and were significantly associated with older age, rural residence, underlying pulmonary conditions, and prescriptions for antibiotics or inhalers. Diagnostic delays for coccidioidomycosis are common, and addressing such delays could improve clinical outcomes.

Snowshoe hare virus (SSHV) is an arbovirus in the California serogroup known to circulate throughout Canada and northern latitudes of the United States. The clinical spectrum of SSHV infection ranges from asymptomatic or mild febrile illness to neuroinvasive disease; neuroinvasive disease occurs more often in children and young adults. We describe a cluster of confirmed and probable SSHV meningoencephalitis cases in 3 children from Whistler, British Columbia, Canada, in the summer of 2024. We highlight the shared epidemiology, clinical manifestations, serologic diagnostic methods, and outcomes for the cases. All 3 children acquired the infection locally and made a full recovery. This case series suggests underrecognized SSHV infection prevalence that warrants enhanced surveillance and review of existing diagnostic algorithms. California serogroup viruses, including SSHV, should be recognized as a potential cause of neuroinvasive disease in North America during mosquito season, particularly when initial diagnostic testing is inconclusive.

Blastomyces urine antigen testing is a sensitive blastomycosis diagnostic method, but its utility for active case identification during outbreaks is unknown. We evaluated urine antigen testing for identifying blastomycosis cases during a 2023 outbreak at a Michigan, USA, paper mill and assessed demographic and clinical factors associated with test positivity. Approximately 2 months after the outbreak was recognized, we collected work and health information for 603 employees; 95% (n = 578) underwent urine antigen testing and 9% (n = 52) tested positive, including 25 previously undetected cases. Blastomycosis-like symptoms were associated with test positivity (p<0.001), but 10% of employees with positive results were asymptomatic. Recent hospitalization for blastomycosis was associated with test positivity (p = 0.02) and higher antigen levels. Further research into urine antigen testing is needed clarify its suitability for detecting mild and asymptomatic infections during outbreak investigations. Urine antigen testing had high acceptability among employees and effectively identified additional cases.

Reports of ocular manifestations of Lyme disease (LD) are uncommon, and signs and symptoms may be overlooked by physicians. We conducted a retrospective case series of ocular LD reported during 1988–2025. Among 27 published reports in PubMed, we noted that, in 38 cases, the most common ocular manifestation was uveitis, representing 45% of cases, followed by optic neuritis and cranial nerve palsies (including trochlear and abducens). Not all cases met Centers for Disease Control and Prevention surveillance guidelines for LD, given that some case reports were published before the current guidelines. Cases that provided microbiologic proof were 2 anterior uveitis cases, 1 case of anterior uveitis with abducens’s nerve palsy, 1 case of intermediate uveitis, and 1 case of intranuclear ophthalmoplegia. Ocular LD can have a broad variety of manifestations; therefore, physicians should be aware of those manifestations and obtain microbiologic proof for a more definitive diagnosis and epidemiologic value when possible.

Group A Streptococcus (GAS) causes a variety of diseases in humans but is not widely appreciated as a cause of meningitis. During 1997–2022, ten sites participating in the Active Bacterial Core Surveillance network in the United States identified GAS meningitis cases. We calculated annual incidence and case-fatality rates (CFRs) for 320 of those cases and determined antimicrobial resistance by whole-genome sequencing. Annual incidence of GAS meningitis ranged from 0.02 to 0.07 cases/100,000 persons. Children <1 year of age had the highest average annual incidence, 0.23 cases/100,000 children. GAS meningitis had a higher CFR (19.4%) than meningitis caused by group B Streptococcus, Streptococcus pneumoniae, Neisseria meningitidis, or Haemophilus influenzae. Clindamycin resistance among GAS meningitis isolates increased from 3.2% during 1997–2002 to 17.7% during 2018–2022. Clinicians should be aware that meningitis is an uncommon but severe manifestation of invasive GAS and has a higher CFR than more established meningitis etiologies.

A previous study demonstrated noninferior efficacy of 4-month rifapentine/moxifloxacin regimen for tuberculosis (TB) treatment compared with the standard regimen. We analyzed pregnancy outcomes of women who became pregnant during the study. Among 740 women, 97 (13.1%) became pregnant. Of 102 pregnancies (in 97 participants), 30 (29.4%) participants were exposed to study drugs. Fetal loss was reported for 3/13 (23.1%) in the control regimen, 1/9 (11.1%) in the rifapentine/moxifloxacin regimen, and 1/8 (12.5%) in the rifapentine regimen. Among 21 live births in exposed pregnancies (7 in each arm), 1 infant with a congenital anomaly was reported in a participant on the rifapentine regimen. Among women receiving a short rifapentine/moxifloxacin regimen for tuberculosis who became pregnant, we observed no elevated rates of fetal losses or congenital anomalies.

Haematospirillum jordaniae was first identified as a human pathogen in 2016. In this article, we describe 4 patients who had H. jordaniae infections identified in 2020 and who had temporally and spatially linked environmental exposures. Three of the 4 patients reported leg injuries while participating in recreational river water activities in south-central Pennsylvania, USA. In 2024, we detected H. jordaniae in river samples collected at locations identified during patient interviews. All patients sought emergency department services for clinical assessment; however, the causative bacterial isolate was not initially identified. H. jordaniae was identified as the bacterial cause months after patient treatment and discharge. Although H. jordaniae infections are considered rare, the true occurrence is unknown. Additional information about the organism’s ecology and environmental seasonality could guide public health messaging and increase awareness among healthcare providers.

Reptile-associated outbreaks of human Salmonella infections are increasing in Canada, coinciding with a rise in the popularity of reptiles as pets. We conducted a retrospective analysis of surveillance data for human Salmonella case-patients in Ontario during 2015–2022. We compared serotypes and reptile types for those reporting domestic reptile or amphibian exposure with veterinary Salmonella isolates reported during the same period. Case-patients commonly reported contact with reptile types from which Salmonella was most frequently isolated. Some serotypes from human case-patients were closely associated with contact with specific reptile types, including Salmonella Paratyphi B biovar Java (Salmonella Paratyphi B variant L (+) tartrate +) with snakes, Salmonella Agbeni with turtles, and Salmonella Cotham, Salmonella Chester, and Salmonella Tennessee with bearded dragons. Salmonella was most likely to be reported from reptiles fed a carnivorous diet. Education of reptile owners could help promote proper veterinary care and reduce transmission of zoonotic infections.

Candida bloodstream infections, and their increasing antifungal resistance, are a global concern. In this cross-sectional study, we analyzed 2,443 culture-confirmed candidemia cases reported in South Africa during 2012–2017 to assess the effect of previous antifungal exposure on nonsusceptible Candida infection. We classified cases by species resistance profile and patient’s antifungal use within 14 days before infection. We found that 48% of cases were caused by nonsusceptible species, and 20% of patients had prior antifungal exposure, mainly to fluconazole. In patients >90 days of age, prior antifungal use was significantly associated with nonsusceptible Candida bloodstream infection (adjusted OR 2.02, 95% CI 1.43–2.87; p<0.001), with species-specific effects. No such association was found in neonates and young infants, for whom hospital transmission appeared more influential. Our findings underscore the need for targeted antifungal stewardship and enhanced infection prevention to mitigate antifungal resistance in South Africa.

The complexity of rickettsial serodiagnostics during acute illness has limited clinical characterization in Africa. We used archived samples from sepsis (n = 259) and acute febrile illness (n = 70) cohorts in Uganda to identify spotted fever and typhus group rickettsiae by using immunofluorescence assay and clinically validated rRNA reverse transcription PCR (RT-PCR). Among 329 participants, 10.0% had rickettsial infections (n = 33; n = 20 identified with immunofluorescence assay and n = 13 by RT-PCR). Serum rRNA RT-PCR was 75.0% (95% CI 42.8–94.5%) sensitive and 91.2% (95% CI 85.8–95.1%) specific. Thrombocytopenia was more common among patients with rickettsial infections than with other nonmalarial infections (adjusted odds ratio 3.7; p = 0.003). No participants were on a tetracycline antimicrobial drug at admission. rRNA RT-PCR is a promising diagnostic strategy for identifying acute rickettsial infections. Doxycycline should be included in empiric antimicrobial drug regimens for nonmalarial febrile illness in this region.