Rickettsial Disease in the US 2025 | Statistics & Facts

Rickettsial Disease in America 2025

Rickettsial diseases represent one of the most significant public health challenges facing the United States in 2025, with cases continuing to surge across multiple regions. These bacterial infections, transmitted primarily through tick bites, have seen a dramatic increase over the past two decades, with reported cases more than tripling since 2000. The major rickettsial diseases affecting Americans include Spotted Fever Rickettsiosis (which encompasses Rocky Mountain Spotted Fever), Ehrlichiosis, Anaplasmosis, and Q Fever. Understanding the current statistics, geographic distribution, and emerging trends is critical for healthcare providers, public health officials, and the general public to combat these potentially fatal infections.

The escalating incidence of rickettsial disease in the US reflects a complex interplay of factors including climate change, expanding tick populations, increased outdoor recreational activities, and improved diagnostic capabilities. From the southeastern states where Ehrlichiosis dominates to the northeastern and upper midwestern regions where Anaplasmosis is most prevalent, these vector-borne illnesses continue to pose serious health risks. With hospitalization rates exceeding 60% for some rickettsial diseases and case-fatality rates reaching 5-10% for Rocky Mountain Spotted Fever when treatment is delayed, the urgency for awareness and early intervention cannot be overstated. This comprehensive analysis presents the latest verified data from US government sources, offering insights into disease patterns, demographic vulnerabilities, and the critical statistics that define the rickettsial disease landscape in America for 2025.

Key Facts About Rickettsial Disease in the US 2025

Data source: CDC National Notifiable Diseases Surveillance System (NNDSS), CDC Rocky Mountain Spotted Fever Statistics, CDC Ehrlichiosis and Anaplasmosis Epidemiology Reports 2023

The data reveals alarming trends in rickettsial disease prevalence across the United States. The documented 300% increase in cases since 2000 represents one of the fastest-growing categories of vector-borne diseases in the nation. Spotted Fever Rickettsiosis remains the predominant concern with over 6,000 cases reported in recent years, though this figure likely underestimates the true burden due to underdiagnosis and underreporting. The seasonal concentration of 68% of cases occurring during the May-August period correlates directly with peak tick activity, particularly nymphal tick stages that are most difficult to detect on the human body.

The fatality statistics are particularly sobering, with Rocky Mountain Spotted Fever maintaining a 5-10% case-fatality rate despite modern medical advances. What makes this especially concerning is that children under 10 years account for less than 6% of cases but represent 22% of all deaths—a disparity attributed to delayed diagnosis and hesitancy among healthcare providers to prescribe doxycycline to young children. The 62% hospitalization rate for RMSF patients places significant strain on healthcare systems, particularly in endemic regions. Meanwhile, the finding that only 53% of patients receive appropriate antibiotic treatment highlights critical gaps in clinical recognition and management protocols that must be addressed through enhanced provider education and public awareness campaigns.

Spotted Fever Rickettsiosis Cases in the US 2023

Data source: CDC Data and Statistics on Spotted Fever Rickettsiosis, National Notifiable Diseases Surveillance System 2023

Spotted Fever Rickettsiosis in the US continues to demonstrate persistently elevated incidence rates through 2023, with approximately 6,463 cases reported nationwide. The incidence rate of 19.4 cases per million population represents nearly a tenfold increase from rates observed in 2000, when only 1.7 cases per million were documented. Notably, confirmed cases comprise only 2.7% of total reports, with the overwhelming majority (97.3%) classified as probable based on single serologic tests rather than more definitive diagnostic methods such as paired serology, PCR, or immunohistochemistry. This diagnostic pattern suggests potential overdiagnosis, as background seroprevalence studies indicate that prior exposure to spotted fever group rickettsia in certain populations may lead to positive antibody tests in patients with unrelated febrile illnesses.

The year-over-year analysis reveals relative stability in case counts from 2019 to 2023, with the notable exception of a 10.8% surge in 2020. While the 2020 spike initially suggested increased disease transmission, epidemiologic investigations indicate this rise likely resulted from enhanced provider awareness following CDC educational initiatives and publication of updated diagnostic guidelines rather than true disease expansion. The subsequent 5% decline in 2021 followed by modest increases in 2022-2023 suggests the disease has reached a new endemic equilibrium at substantially higher levels than historical baselines. The consistently low proportion of confirmed cases (2.7-3.2%) underscores ongoing challenges in species-specific rickettsial diagnosis, as most healthcare facilities rely on indirect immunofluorescence assays that cannot distinguish between Rickettsia rickettsii (the cause of Rocky Mountain Spotted Fever) and less pathogenic species like Rickettsia parkeri or Rickettsia 364D.

Geographic Distribution of Spotted Fever Rickettsiosis in the US 2023

Data source: CDC Spotted Fever Rickettsiosis Geographic Data 2023, State Health Department Surveillance Reports

The geographic distribution of Spotted Fever Rickettsiosis reveals stark regional disparities, with southern and south-central states bearing a disproportionate disease burden. Arkansas leads the nation with an extraordinary incidence rate of 29.5 cases per 100,000 population—more than 150 times the national average. North Carolina reports the highest absolute case count with 1,124 cases in 2023, reflecting both its large population and endemic transmission. The Tennessee, Missouri, and Oklahoma corridor represents a geographic hotspot where environmental conditions, tick populations, and human exposure patterns converge to maintain elevated transmission rates. Notably, these states share ecological characteristics including mixed deciduous forests, moderate climates, and abundant white-tailed deer populations that serve as primary hosts for tick vectors.

The regional analysis illuminates the critical role of tick species distribution in disease epidemiology. The American dog tick (Dermacentor variabilis) and lone star tick (Amblyomma americanum) predominate in high-incidence southeastern states, with the latter species experiencing significant range expansion northward over the past two decades. This expansion correlates with increased case reports in previously low-incidence areas. The Western states report markedly lower incidence (0.4 cases per 100,000) despite the presence of Dermacentor andersoni, the Rocky Mountain wood tick, which historically gave the disease its name. This paradox suggests that factors beyond tick presence—including human behavior patterns, tick density, and rickettsial infection rates in tick populations—determine disease risk. The cases per square mile metric highlights that disease concentration doesn’t simply reflect population density but rather complex ecological factors that facilitate tick-human encounters in specific geographic corridors.

Ehrlichiosis Cases in the US 2023

Data source: CDC Ehrlichiosis Epidemiology and Statistics, NNDSS Annual Tables 2023

Ehrlichiosis cases in the United States demonstrate a steady upward trajectory through 2023, with 2,435 total cases reported—a 11.1% increase from 2019 levels. Ehrlichia chaffeensis, the causative agent of human monocytic ehrlichiosis, accounts for approximately 92% of all ehrlichiosis cases, with 2,244 cases in 2023 alone. This species, transmitted primarily by the lone star tick (Amblyomma americanum), has become increasingly prevalent as this aggressive tick species expands its geographic range from traditional southeastern strongholds into the midwest and northeastern United States. E. ewingii infections remain relatively rare with only 43 confirmed cases in 2023, though this figure likely underestimates true prevalence given diagnostic limitations in distinguishing between ehrlichial species using standard serologic methods.

The five-year trend reveals ehrlichiosis incidence remained remarkably consistent despite the COVID-19 pandemic, which disrupted surveillance for many reportable diseases. The incidence rate increased from 6.6 per million in 2019 to 7.3 per million in 2023, representing a 10.6% growth over the period. This sustained increase contrasts with other tickborne diseases that showed more pronounced pandemic-related reporting decreases, suggesting ehrlichiosis may be less susceptible to surveillance artifacts or represents genuine disease expansion. Undetermined ehrlichiosis cases (where specific species cannot be identified) comprise approximately 6% of reports, down from historical levels exceeding 10%, reflecting improvements in laboratory diagnostic capabilities. The geographic distribution mirrors lone star tick habitat, with Arkansas, Missouri, Oklahoma, Virginia, and North Carolina reporting the highest case counts and incidence rates in the South Central and Southeastern regions.

Ehrlichiosis by Demographics and Clinical Outcomes in the US 2023

Data source: CDC Ehrlichiosis Data and Statistics 2019-2023, Tickborne Rickettsial Disease Case Report Forms

The demographic profile of ehrlichiosis in the US reveals significant age-related vulnerability patterns, with adults aged 40-79 years accounting for nearly 64% of all cases. While absolute case numbers peak in the 40-59 year age bracket with 828 cases, the incidence rate is highest among those 60-79 years at 18.4 cases per million—more than 15 times the rate in children under 10 years. This age distribution reflects cumulative occupational and recreational tick exposure over decades of outdoor activity. Children demonstrate lower incidence but concerning clinical outcomes, as immunologic naivety may contribute to more severe presentations despite lower infection rates. The pronounced male predominance with a 1.9:1 ratio (65% male versus 35% female) aligns with occupational exposure patterns, as men disproportionately work in outdoor industries including forestry, landscaping, and agriculture where tick encounters are frequent.

The hospitalization rate of 61.1% underscores the serious nature of ehrlichiosis, requiring intensive medical management in the majority of cases. Intensive care unit admission occurs in 6% of hospitalized patients, typically due to complications including respiratory failure, acute kidney injury, or hemophagocytic lymphohistiocytosis syndrome. The overall case-fatality rate of 0.5% (12 deaths in 2023) remains low but represents entirely preventable mortality with prompt doxycycline therapy. Notably, ehrlichiosis follows a pronounced seasonal pattern with 72.2% of cases occurring during the May-August period when lone star tick nymphs and adults are most active. This temporal clustering provides clear opportunities for targeted prevention messaging and heightened clinical suspicion during peak months. The 20% of cases occurring in September-November corresponds to adult tick activity, while off-season cases (7.8%) may represent delayed diagnosis, atypical exposures, or infections acquired in warmer southern regions where tick activity extends year-round.

Anaplasmosis Cases in the US 2023

Data source: CDC Anaplasmosis Epidemiology and Statistics, NNDSS 2023 Data Tables

Anaplasmosis cases reached 6,017 in 2023, marking the highest annual case count since the disease became nationally notifiable in 1999. The incidence rate of 18.1 cases per million population represents a more than 20-fold increase from rates observed at the turn of the century. This dramatic surge reflects multiple converging factors including geographic expansion of Ixodes scapularis (blacklegged tick) populations, increased outdoor recreation participation, climate change impacts on tick survival and activity periods, and enhanced laboratory diagnostic capacity. The 2020 decline to 4,008 cases represents an anomaly attributed to COVID-19 pandemic-related reductions in healthcare-seeking behavior and diagnostic testing rather than true disease decrease, as evidenced by the rapid 30.1% rebound in 2021.

The proportion of confirmed versus probable cases has remained remarkably stable across the five-year period, with approximately 22% meeting stringent confirmation criteria including PCR detection, immunohistochemical demonstration, culture isolation, or fourfold antibody titer rise in paired sera. The remaining 78% of probable cases rely on single-point elevated IgG antibody titers, which some experts argue may overestimate true disease burden due to background seroprevalence in endemic regions. However, the consistency of this ratio over time and the correlation with other surveillance indicators suggest most probable cases represent genuine infections. The disease’s geographic footprint continues expanding beyond traditional Northeast and Upper Midwest strongholds, with emerging endemic foci now documented in mid-Atlantic states and isolated cases reported from previously non-endemic western regions, signaling ongoing ecological changes favoring Ixodes tick establishment in new territories.

Geographic and Seasonal Distribution of Anaplasmosis in the US 2023

Data source: CDC Anaplasmosis Statistics 2019-2023, State Health Department Reports

The geographic distribution of anaplasmosis reveals two primary endemic corridors: the Upper Midwest (Minnesota, Wisconsin) and the Northeast (Maine through New York). Minnesota leads nationally with 1,342 cases and an incidence rate of 23.7 per 100,000—more than 130 times the national average. Maine demonstrates the highest state-level incidence at 30.2 per 100,000, reflecting intense Ixodes scapularis tick populations in coastal and forested regions. Together, the Midwest and Northeast regions account for 90.7% of all anaplasmosis cases (5,455 of 6,017 cases) in 2023, with the remaining cases scattered across emerging endemic areas where blacklegged tick populations are newly establishing.

The five-year trend analysis reveals explosive growth across multiple states, with Pennsylvania experiencing a remarkable 68% increase and Maine showing a 56% surge between 2018-2023. This expansion reflects northward and westward migration of Ixodes tick populations driven by climate warming, white-tailed deer range expansion, and landscape fragmentation that increases edge habitats favorable for tick survival. The seasonal concentration demonstrates remarkable consistency across states, with 65-72% of cases occurring during the May-August period when nymphal Ixodes ticks—the primary vector life stage for anaplasmosis—quest most actively for blood meals. Peak infection risk occurs in June and July when nymphs reach peak density and humans engage in maximal outdoor recreation. The emergence of 562 cases in non-traditional regions including mid-Atlantic states, Ohio River Valley, and isolated Western states signals ongoing geographic expansion that warrants enhanced surveillance and provider education in these transitioning areas.

Q Fever Cases in the US 2019-2023

Data source: CDC Q Fever Epidemiology and Statistics, Acute and Chronic Q Fever National Surveillance 2008-2023

Q Fever caused by Coxiella burnetii represents a relatively uncommon but significantly underdiagnosed rickettsial disease in the United States, with an average of 192 cases reported annually from 2019-2023. The incidence rate of approximately 0.60 cases per million population has remained stable over the five-year period, though epidemiologic evidence suggests this represents substantial underreporting. A landmark study comparing CDC surveillance data with commercial laboratory testing found that CDC-reported acute Q fever cases were only one-third the number identified through private laboratory systems, suggesting the true burden may exceed 500-600 annual cases. The acute-to-chronic case ratio of approximately 5.5:1 (average 163 acute versus 31 chronic cases annually) aligns with clinical understanding that less than 5% of infected individuals progress to chronic disease.

The consistently elevated hospitalization rate averaging 52.5% underscores the severity of clinically apparent Q fever. Unlike other rickettsial diseases where hospitalization occurs primarily in complicated cases, Q fever’s high admission rate reflects the severity of acute presentations including pneumonia, hepatitis, and fever of unknown origin requiring extensive diagnostic evaluation. Chronic Q fever, while rare, carries grave prognosis with manifestations including endocarditis (the most common chronic form), vascular graft infections, and osteomyelitis. The case-fatality rate for acute Q fever approximates 2% but increases to 30-60% in chronic disease without appropriate prolonged antimicrobial therapy. The pandemic years (2020-2021) showed modest case declines (170 and 187 cases respectively), likely reflecting reduced healthcare-seeking behavior and diagnostic testing rather than decreased transmission, as Coxiella burnetii transmission through aerosols from infected livestock is unlikely to have been substantially impacted by pandemic public health measures.

Geographic and Occupational Distribution of Q Fever in the US 2019-2023

Data source: CDC Q Fever in the United States Summary 2000-2023, State Health Department Reports

The geographic distribution of Q Fever demonstrates clear correlation with livestock-rearing regions, particularly Western and Great Plains states which collectively account for 63.3% of cases. California, Texas, and Iowa report the highest absolute case numbers with 187, 142, and 86 cases respectively over the five-year period, reflecting their substantial dairy, cattle, and mixed livestock industries. However, when adjusted for population, Wyoming demonstrates the highest incidence at 4.14 cases per million—more than 6.5 times the national average—followed closely by Montana at 3.17 per million and Iowa at 2.72 per million. These states share characteristics including high sheep and cattle density, rural populations with frequent livestock contact, and arid climates that facilitate Coxiella burnetii survival in the environment.

Occupational analysis reveals that approximately 40% of Q fever cases report direct livestock-related employment including ranching, dairy farming, veterinary medicine, and livestock processing. However, 61% of cases reported no direct animal exposure, underscoring Coxiella burnetii’s remarkable ability to spread via windborne transmission from contaminated environments. Studies demonstrate viable organisms can travel 1-2 miles from parturition sites, explaining infections in urban and suburban residents with no obvious animal contact. The disease shows distinct seasonality with peak incidence in April-June corresponding to parturition seasons for cattle, sheep, and goats when massive quantities of organisms are shed in birth products and amniotic fluids. Sporadic cases throughout the year reflect diverse exposure routes including consumption of unpasteurized dairy products (8.4% of cases reported raw milk consumption—nearly 3 times the 3% national baseline), laboratory exposures, and travel to endemic regions internationally. The relatively low case counts in non-agricultural regions suggest either underdiagnosis due to low clinical suspicion or genuine reduced transmission in areas with minimal livestock presence.

Rickettsial Disease Fatality and Severe Outcomes in the US 2023

Disclaimer: This research report is compiled from publicly available sources. While reasonable efforts have been made to ensure accuracy, no representation or warranty, express or implied, is given as to the completeness or reliability of the information. We accept no liability for any errors, omissions, losses, or damages of any kind arising from the use of this report.

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