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Rickettsia parkeri rickettsiosis is an emerging, tick-borne disease in the United States (US), transmitted by the bite of Amblyomma maculatum group ticks. Clinical manifestations include fever, headache, myalgia, maculopapular rash, and a characteristic eschar that forms at the site of the tick bite. Arizona's index case of R. parkeri rickettsiosis was reported in 2014. Seven additional confirmed and probable cases were identified during 2016-2017 through routine investigation of electronic laboratory reports and by self-reporting to public health authorities. Serum samples were evaluated for immunoglobulin G antibodies reactive with antigens of Rickettsia rickettsii (the agent of Rocky Mountain spotted fever [RMSF]) and R. parkeri using indirect immunofluorescence antibody tests. Eschar swab specimens were evaluated using Rickettsia genus-specific and R. parkeri-specific real-time PCR assays. Patients (six male, one female) ranged in age from 29 to 69 years (median of 41 years), and became ill between July 2016 and September 2017. Fever (6/7), myalgia (5/7), and arthralgia (5/7) were most commonly reported and 5/7 patients had a documented eschar. All patients reported a tick bite acquired in southern Arizona within 2-8 days before illness onset. Four patients worked as U.S. Border Patrol agents. Antibodies reactive to R. rickettsii, R. parkeri, or to both antigens were detected in all patients. Seroconversions between acute and convalescent-phase samples were identified for two patients and DNA of R. parkeri was identified in eschar swab samples from two patients. R. parkeri rickettsiosis is endemic to a region of the southwestern United States and presents an occupational risk that could be lessened by prevention messaging to Border Patrol agents. RMSF, a closely related and more severe spotted fever rickettsiosis, is also endemic to Arizona. Public health agencies can assist clinicians in distinguishing these two infections clinically through education and accessing species-specific diagnostic assays that can improve surveillance efforts for both diseases.

BackgroundSince 2000, the reported prevalence of tick-borne spotted fever rickettsiosis has increased considerably. We compared the level of antibody reactivity among healthy blood donors from 2 widely separated regions of the United States and evaluated the impact of antibody prevalence on public health surveillance in one of these regions.MethodsDonor serum samples were evaluated by indirect immunofluorescence antibody assay to identify immunoglobulin G (IgG) antibodies reactive with Rickettsia rickettsii. The Georgia Department of Public Health (GDPH) analyzed characteristics of cases from 2016 surveillance data to evaluate the utility of laboratory surveillance for case assessment.ResultsOf the Georgia donors (n = 1493), 11.1% demonstrated antibody titers reactive with R. rickettsii at titers ≥64, whereas 6.3% of donors from Oregon and Washington (n = 1511) were seropositive. Most seropositive donors had a titer of 64; only 3.1% (n = 93) of all donors had titers ≥128. During 2016, GDPH interviewed 243 seropositive case patients; only 28% (n = 69) met inclusion criteria in the national case definition for spotted fever rickettsiosis.ConclusionsThese findings suggest that a single IgG antibody titer is an unreliable measure of diagnosis and could inaccurately affect surveillance estimates that define magnitude and clinical characteristics of Rocky Mountain spotted fever and other spotted fever rickettsioses.

Chikungunya, a mosquito-borne viral, acute febrile illness (AFI) is associated with polyarthralgia and polyarthritis. Differentiation from other AFI is difficult due to the non-specific presentation and limited availability of diagnostics. This 3-year study identified independent clinical predictors by day post-illness onset (DPO) at presentation and age-group that distinguish chikungunya cases from two groups: other AFI and dengue. Specimens collected from participants with fever ≤7 days were tested for chikungunya, dengue viruses 1–4, and 20 other pathogens. Of 8,996 participants, 18.2% had chikungunya, and 10.8% had dengue. Chikungunya cases were more likely than other groups to be older, report a chronic condition, and present, Author summary Chikungunya is an acute febrile illness (AFI), caused by the chikungunya virus (CHIKV), that is transmitted by mosquitoes. Patients with chikungunya exhibit joint, muscle, or bone pain, and may also have skin rash, red eyes (conjunctiva), and red swollen joints (arthritis). Up to 20% of cases develop long lasting arthritis, fatigue or psychiatric conditions. We used data from our prospective study to identify signs and symptoms that predict chikungunya. We enrolled 8,996 AFI patients and tested for CHIKV, dengue viruses 1–4 (DENV 1–4), and other pathogens. A pathogen was detected in 55% of participants; 18.2% had CHIKV and 10.8% had DENV 1–4 infections. This study compared the clinical presentation of chikungunya with that of all other AFI and dengue alone. Regardless of timing of presentation, significant predictors of chikungunya were joint pain, muscle, bone or back pain, and red conjunctiva when compared to other AFI, and arthritis, joint pain, skin rash, any bleeding, and irritability, when dengue was the comparator group. Chikungunya patients were less likely than AFI and dengue patients to have low platelets, signs of poor circulation, diarrhea, headache, and cough. By enrolling febrile patients at presentation, we identified unbiased predictors of chikungunya. These findings can assist physicians to clinically diagnose chikungunya and initiate proper patient management.

The likely vector was Amblyomma triste, a Neotropical tick species only recently recognized in the United States., In the United States, all previously reported cases of Rickettsia parkeri rickettsiosis have been linked to transmission by the Gulf Coast tick (Amblyomma maculatum). Here we describe 1 confirmed and 1 probable case of R. parkeri rickettsiosis acquired in a mountainous region of southern Arizona, well beyond the recognized geographic range of A. maculatum ticks. The likely vector for these 2 infections was identified as the Amblyomma triste tick, a Neotropical species only recently recognized in the United States. Identification of R. parkeri rickettsiosis in southern Arizona demonstrates a need for local ecologic and epidemiologic assessments to better understand geographic distribution and define public health risk. Education and outreach aimed at persons recreating or working in this region of southern Arizona would improve awareness and promote prevention of tickborne rickettsioses.

An evaluation of chitosan gelling fibre dressing (KytoCel, Aspen Medical) was undertaken by tissue viability nurses in a large acute trust from December 2014—May 2015. The aim of this evaluation was to examine whether the gelling-fibre dressing can improve healing outcomes—reduction of bioburden and promotion of wound healing in both acute and chronic wounds that are infected or critically colonised. A total of 20 patients were recruited with acute and other complex wounds where wound infection was already established, or an excessive wound bioburden was delaying healing. Wound swabs were taken before and after dressing application between days 1, 3, 5 and 11 when clinically indicated, or at the surgical and medical teams' request. No more than two sets of swabs were taken in all patients. The evaluation incorporated three main criteria: patient baseline data, dressing performance, and patient perspective. Key findings were a significant reduction in wound size; rapid improvement of the quality of granulation tissue in 11 patients (55%), the reduction of the wound bioburden, and malodour combined with effective exudate management. The investigators also wanted to establish if there was a significant reduction in the identified bacteria from the initial wound swab results. Some patients were on systemic antibiotic therapy, their reduction in bacteria species may also be related to secondary dressings used. More robust investigation may be required to establish if the bacterial reduction was a result of the primary dressing.

Coxiella burnetii is a zoonotic pathogen that causes Q fever in humans and is transmitted primarily from infected goats, sheep, or cows. Q fever typically presents as an acute febrile illness; however, individuals with certain predisposing conditions, including cardiac valvulopathy, are at risk for chronic Q fever, a serious manifestation that may present as endocarditis. In response to a cluster of Q fever cases detected by public health surveillance, we evaluated C. burnetii infection in a community that operates a large-scale cow and goat dairy. A case was defined as an individual linked to the community with a C. burnetii phase II IgG titer ≥ 128. Of 135 participants, 47 (35%) cases were identified. Contact with or close proximity to cows, goats, and their excreta was associated with being a case (relative risk 2.7, 95% confidence interval 1.3-5.3). Cases were also identified among individuals without cow or goat contact and could be related to windborne spread or tracking of C. burnetii on fomites within the community. A history of injection drug use was reported by 26/130 (20%) participants; follow-up for the presence of valvulopathy and monitoring for development of chronic Q fever may be especially important among this population.

background Rocky Mountain spotted fever is a life-threatening, tick-borne disease caused by Rickettsia rickettsii . This disease is rarely reported in Arizona, and the principal vectors, Dermacentor species ticks, are uncommon in the state. From 2002 through 2004, a focus of Rocky Mountain spotted fever was investigated in rural eastern Arizona. methods We obtained blood and tissue specimens from patients with suspected Rocky Mountain spotted fever and ticks from patients’ homesites. Serologic, molecular, immunohistochemical, and culture assays were performed to identify the causative agent. On the basis of specific laboratory criteria, patients were classified as having confirmed or probable Rocky Mountain spotted fever infection. results A total of 16 patients with Rocky Mountain spotted fever infection (11 with confirmed and 5 with probable infection) were identified. Of these patients, 13 (81 percent) were children 12 years of age or younger, 15 (94 percent) were hospitalized, and 2 (12 percent) died. Dense populations of Rhipicephalus sanguineus ticks were found on dogs and in the yards of patients’ homesites. All patients with confirmed Rocky Mountain spotted fever had contact with tick-infested dogs, and four had a reported history of tick bite preceding the illness. R. rickettsii DNA was detected in nonengorged R. sanguineus ticks collected at one home, and R. rickettsii isolates were cultured from these ticks. conclusions This investigation documents the presence of Rocky Mountain spotted fever in eastern Arizona, with common brown dog ticks ( R. sanguineus ) implicated as a vector of R. rickettsii . The broad distribution of this common tick raises concern about its potential to transmit R. rickettsii in other settings.

Ehrlichiosis is a tick-borne disease that ranges in severity from asymptomatic infection to fatal sepsis. Ehrlichiosis acquired from transfusion of blood products has not been documented in the literature to date. A case of Ehrlichia ewingii infection likely transmitted by transfusion of leukoreduced platelets is described, and public health implications are discussed.

Serum samples from people exposed to sheep at a research facility were evaluated by a commercial laboratory and resulted in an overall Coxiella burnetii seroprevalence of 75%. We interviewed individuals to determine exposure history and compatible illness, and retested their sera. Analysis indicated that the commercial laboratory was misinterpreting its results; when corrected, the seroprevalence dropped to 27%. Test kits of the brand used by the commercial laboratory gave equivalent results to the in-house CDC assay when tested in parallel at CDC. Upon final analysis, only the attending veterinarian was confirmed as a Q fever case. This event resulted in increased risk reduction protocols at the research facility and improved public health communication among health authorities. This pseudoepidemic resulted from a lapse in laboratory quality control for testing. Similar errors can be avoided through standardization and improved review of laboratory procedures.

Rickettsialpox, a spotted fever rickettsiosis, was first identified in New York City (NYC) in 1946. During the next five years, approximately 540 additional cases were identified in NYC. However, during the subsequent five decades, rickettsialpox received relatively little attention from clinicians and public health professionals, and reporting of the disease diminished markedly. During February 2001 through August 2002, 34 cases of rickettsialpox in NYC were confirmed at CDC from cutaneous biopsy specimens tested by using immunohistochemical (IHC) staining, PCR analysis, and isolation of Rickettsia akari in cell culture, as well as an indirect immunofluorescence assay of serum specimens. Samples were collected from patients with febrile illnesses accompanied by an eschar, a papulovesicular rash, or both. Patients originated predominantly from two boroughs (Manhattan and the Bronx). Only 8 (24%) of the cases were identified prior to the reports of bioterrorism-associated anthrax in the United States during October 2001, and lesions of several patients evaluated during and subsequent to this episode were suspected initially to be cutaneous anthrax. IHC staining of biopsy specimens of eschars and papular lesions were positive for spotted fever group rickettsiae for 32 patients. Of the eleven patients for whom paired serum samples were obtained, all demonstrated fourfold or greater increases in antibody titers reactive with R. akari. The 17-kDa protein gene sequence of R. akari was amplified from eschars of five patients. Four isolates of R. akari were obtained from cutaneous lesions. Possible factors responsible for the increase in clinical samples evaluated for rickettsialpox during this interval include renewed clinical interest in the disease, improved diagnostic methods, epizootiological influences, and factors associated with the recent specter of bioterrorism.

Identifying etiologies of acute febrile illnesses (AFI) is challenging due to non-specific presentation and limited availability of diagnostics. Prospective AFI studies provide a methodology to describe the syndrome by age and etiology, findings that can be used to develop case definitions and multiplexed diagnostics to optimize management. We conducted a 3-year prospective AFI study in Puerto Rico. Patients with fever ≤7 days were offered enrollment, and clinical data and specimens were collected at enrollment and upon discharge or follow-up. Blood and oro-nasopharyngeal specimens were tested by RT-PCR and immunodiagnostic methods for infection with dengue viruses (DENV) 1–4, chikungunya virus (CHIKV), influenza A and B viruses (FLU A/B), 12 other respiratory viruses (ORV), enterovirus, Leptospira spp., and Burkholderia pseudomallei. Clinical presentation and laboratory findings of participants infected with DENV were compared to those infected with CHIKV, FLU A/B, and ORV. Clinical predictors of laboratory-positive dengue compared to all other AFI etiologies were determined by age and day post-illness onset (DPO) at presentation. Of 8,996 participants enrolled from May 7, 2012 through May 6, 2015, more than half (54.8%, 4,930) had a pathogen detected. Pathogens most frequently detected were CHIKV (1,635, 18.2%), FLU A/B (1,074, 11.9%), DENV 1–4 (970, 10.8%), and ORV (904, 10.3%). Participants with DENV infection presented later and a higher proportion were hospitalized than those with other diagnoses (46.7% versus 27.3% with ORV, 18.8% with FLU A/B, and 11.2% with CHIKV). Predictors of dengue in participants presenting, Author summary We conducted a prospective study of acute febrile illness (AFI) in Puerto Rico to better understand the etiology of AFI among all age groups in the tropics. Such findings could assist clinicians to identify disease-specific characteristics, which can then be used to initiate proper patient management. We enrolled 8,996 AFI patients and tested them for dengue viruses 1–4 (DENV 1–4) and 21 other pathogens. A pathogen was detected in 55% of patients, most frequently chikungunya virus (CHIKV, 18%), influenza A or B virus (FLU A/B, 12%), DENV 1–4 (11%), or another respiratory virus (ORV, 10%). Participants with dengue presented later after symptom onset and were hospitalized more often (47%) than patients with another etiology of AFI (27% with ORV, 19% with FLU A/B, and 11% with CHIKV). Predictors of patients with dengue differed by timing of presentation but included eye pain, nausea, and low white blood cell or platelet counts; negative predictors included symptoms of respiratory illness. By enrolling febrile patients at clinical presentation, we identified unbiased predictors of patients with dengue as compared to other common AFI. Findings can be used to diagnose dengue patients to provide early and appropriate clinical management.

Rickettsia parkeri, a newly recognized tick-borne pathogen of humans in the Americas, is a confirmed cause of spotted fever group rickettsiosis in Argentina. Until recently, almost all cases of R. parkeri rickettsiosis in Argentina have originated from the Paraná River Delta, where entomological surveys have identified populations of R. parkeri-infected Amblyomma triste ticks. In this report, we describe confirmed cases of R. parkeri rickettsiosis from Córdoba and La Rioja provinces, which are located several hundred kilometers inland, and in a more arid ecological region, where A. triste ticks do not occur. Additionally, we identified questing A. tigrinum ticks naturally infected with R. parkeri in Córdoba province. These data provide evidence that another human-biting tick species serves as a potential vector of R. parkeri in Argentina and possibly, other countries of South America. Fil: Romer, Yamila. Gobierno de la Ciudad de Buenos Aires. Hospital de Infecciosas "Dr. Francisco Javier Muñiz"; Argentina Fil: Nava, Santiago. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Santa Fe. Estación Experimental Agropecuaria Rafaela; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina Fil: Godevic, Francisco. Sanatorio Allende; Argentina Fil: Cicuttin, Gabriel. Instituto de Zoonosis Luis Pasteur; Argentina Fil: Denison, Amy M.. Centers for Disease Control and Prevention. Infectious Diseases Pathology Branch and Rickettsial Zoonoses Branch; Estados Unidos Fil: Singleton, Joseph. Centers for Disease Control and Prevention. Infectious Diseases Pathology Branch and Rickettsial Zoonoses Branch; Estados Unidos Fil: Jelly, Aubree J.. Centers for Disease Control and Prevention. Infectious Diseases Pathology Branch and Rickettsial Zoonoses Branch; Estados Unidos Fil: Kato, Cecilia Y.. Centers for Disease Control and Prevention. Infectious Diseases Pathology Branch and Rickettsial Zoonoses Branch; Estados Unidos Fil: Paddock, Christopher D.. Centers for Disease Control and Prevention. Infectious Diseases Pathology Branch and Rickettsial Zoonoses Branch; Estados Unidos

Among 13 suspected Rocky Mountain spotted fever (RMSF) cases identified through an enhanced surveillance program in Tennessee, antibodies to Rickettsia rickettsii were detected in 10 (77%) patients using a standard indirect immunofluorescent antibody (IFA) assay. Immunoglobulin M (IgM) antibodies were observed for 6 of 13 patients (46%) without a corresponding development of IgG, and for 3 of 10 patients (30%) at least 1 year post-onset. However, recent infection with a spotted fever group rickettsiae could not be confirmed for any patient, based on a lack of rising antibody titers in properly timed acute and convalescent serologic specimens, and negative findings by polymerase chain reaction testing. Case definitions used in national surveillance programs lack specificity and may capture cases that do not represent current rickettsial infections. Use of IgM antibodies should be reconsidered as a basis for diagnosis and public health reporting of RMSF and other spotted fever group rickettsiae in the United States.

The clinical course and laboratory evaluation of 21 patients coinfected with human immunodeficiency virus (HIV) and Ehrlichia chaffeensis or Ehrlichia ewingii are reviewed and summarized, including 13 cases of ehrlichiosis caused by E. chaffeensis, 4 caused by E. ewingii, and 4 caused by either E. chaffeensis or E. ewingii. Twenty patients were male, and the median CD4(+) T lymphocyte count was 137 cells/microL. Exposures to infecting ticks were linked to recreational pursuits, occupations, and peridomestic activities. For 8 patients, a diagnosis of ehrlichiosis was not considered until > or =4 days after presentation. Severe manifestations occurred more frequently among patients infected with E. chaffeensis than they did among patients infected with E. ewingii, and all 6 deaths were caused by E. chaffeensis. Ehrlichiosis may be a life-threatening illness in HIV-infected persons, and the influence of multiple factors, including recent changes in the epidemiology and medical management of HIV infection, may increase the frequency with which ehrlichioses occur in this patient cohort.

Ehrlichia chaffeensis was sought among patients with a history of tick exposure and fever, and the accuracy of other diagnostic tests was compared with that of primary isolation. Among the 38 patients enrolled, E. chaffeensis was isolated from the blood of 7 (18%) and from cerebrospinal fluid specimens of 2 of these 7. All 7 patients also were positive by polymerase chain reaction (PCR) of blood, and 6 patients developed diagnostic titers of antibody to E. chaffeensis. The isolates were characterized by molecular analysis of the 16S rRNA gene, the 120-kDa protein gene, and the variable-length PCR target (VLPT) of E. chaffeensis. On the basis of the 120-kDa and VLPT genotypes, the cerebrospinal fluid and blood isolates from the same patients were identical. This study demonstrates that both PCR and culture of blood for E. chaffeensis have high diagnostic yields. More frequent isolation of E. chaffeensis from patients with infection should further our understanding of the pathogenesis of this infection.

BACKGROUND: Tick-borne illnesses were diagnosed in a group of National Guard members, including some who had donated blood a few days before the onset of symptoms. A voluntary recall of those blood components was issued and a multistate investigation was conducted to determine if transfusion-transmitted illness had occurred. STUDY DESIGN AND METHODS: Donors and recipients were asked to complete questionnaires regarding symptoms and risk factors for infection and to provide blood samples for laboratory analysis. RESULTS: Among National Guard personnel who donated blood, 12 individuals were found to have a confirmed or probable case of Rocky Mountain spotted fever or ehrlichiosis. A total of 320 units (platelets or packed red cells) from 377 donors were transfused into 129 recipients. Although 10 recipients received units from National Guard personnel with confirmed or probable infection, none became ill. CONCLUSION: Transfusion-transmitted illness did not occur. Despite the awareness of the risk for tick-borne diseases and the use of tick-preventive measures, many National Guard personnel reported exposure to ticks. In addition to augmenting current tick-preventive measures, scheduling blood drives before rather than after field exercises could further reduce the potential for transmission of tick-borne pathogens.

Several spotted fever group rickettsiae (SFGR) previously believed to be nonpathogenic are speculated to contribute to infections commonly misdiagnosed as Rocky Mountain spotted fever (RMSF) in the United States, but confirmation is difficult in cases with mild or absent systemic symptoms. We report an afebrile rash illness occurring in a patient 4 days after being bitten by a Rickettsia montanensis-positive Dermacentor variabilis tick. The patient's serological profile was consistent with confirmed SFGR infection.

Recrudescent Rickettsia prowazekii infection, also known as Brill-Zinsser disease, can manifest decades after untreated primary infection but is rare in contemporary settings. We report the first known case of Brill-Zinsser disease in a patient originally infected with a zoonotic strain of R. prowazekii acquired from flying squirrels.

Background Rickettsialpox is a self-limited febrile illness with skin lesions that may be mistaken for signs of potentially more serious diseases, such as cutaneous anthrax or chickenpox. The cluster of cutaneous anthrax cases from bioterrorism in October 2001 likely heightened awareness of and concern for cutaneous eschars. Objectives To apply an immunohistochemical technique on paraffin-embedded skin biopsy specimens for diagnosing rickettsialpox, and to compare the reported incidence of rickettsialpox before, during, and after the cluster of cutaneous anthrax cases. Design Case series. Setting Dermatology department in a large tertiary care hospital in New York City. Patients Eighteen consecutive patients with the clinical diagnosis of rickettsialpox from February 23, 2001, through October 31, 2002. Main Outcome Measures Results of immunohistochemical testing of skin biopsy specimens and of serological testing. Results Immunohistochemical testing revealed spotted fever group rickettsiae in all 16 eschars and in 5 of the 9 papulovesicles tested. A 4-fold or greater increase in IgG antibody titers reactive with Rickettsia akari was observed in all 9 patients for whom acute and convalescent phase samples were available; 6 patients had single titers indicative of rickettsialpox infection (≥1:64). Of the 18 patients, 9 (50%) presented in the 5 months following the bioterrorism attacks. Conclusions Rickettsialpox remains endemic in New York City, and the bioterrorism attacks of October 2001 may have led to increased awareness and detection of this disease. Because rickettsialpox may be confused with more serious diseases, such as cutaneous anthrax or chickenpox, clinicians should be familiar with its clinical presentation and diagnostic features. Immunohistochemical staining of skin biopsy specimens, particularly from eschars, is a sensitive technique for confirming the clinical diagnosis.

Rocky Mountain spotted fever (RMSF) is the most severe tickborne infection in the United States and is a nationally notifiable disease. Since 1981, the annual case-fatality ratio for RMSF has been determined from laboratory-confirmed cases reported to the Centers for Disease Control and Prevention (CDC). Herein, a description is given of patients with fatal, serologically unconfirmed RMSF for whom a diagnosis of RMSF was established by immunohistochemical (IHC) staining of tissues obtained at autopsy. During 1996-1997, acute-phase serum and tissue samples from patients with fatal disease compatible with RMSF were tested at the CDC. As determined by indirect immunofluorescence assay, no patient serum demonstrated IgG or IgM antibodies reactive with Rickettsia rickettsii at a diagnostic titer (i.e., >/=64); however, IHC staining confirmed diagnosis of RMSF in all patients. Polymerase chain reaction validated the IHC findings for 2 patients for whom appropriate samples were available for testing. These findings suggest that dependence on serologic assays and limited use of IHC staining for confirmation of fatal RMSF results in underestimates of mortality and of case-fatality ratios for this disease.

Summary Q fever was diagnosed in a previously healthy man who had recently traveled to the East Coast of Australia. The patient experienced fever and headache accompanied by lymphopenia and elevated liver enzymes but not pneumonia. He had no known direct exposures to animals, exhibited IgM and IgG seroconversion to phase II antigen of Coxiella burnetii and IgM only to phase I antigen, and responded to doxycycline treatment. This case serves as a reminder to clinicians to consider Q fever in the differential diagnosis of acute febrile illness in travelers returning from endemic areas.

Ehrlichiosis due to Ehrlichia chaffeensis usually occurs sporadically or in small clusters, with an annual incidence estimated at 3 to 5 cases per 100,000 population in areas of endemic disease. The putative principal vector is the Lone Star tick (Amblyomma americanum). We investigated an outbreak of ehrlichiosis that occurred in June 1993 among members of a golf-oriented retirement community (community A) in Tennessee. The community is densely wooded and borders a wildlife-management area where deer are numerous.We conducted a case-control study, using medical-history reviews, serologic testing, and testing with the polymerase chain reaction for E. chaffeensis infection. We also surveyed a sample of 10 percent of the households in community A and in another golf-oriented community (community B) more than 20 miles (32 km) from the wildlife-management area. Survey participants completed a questionnaire and provided specimens for serologic testing. In both communities, searches for ticks were undertaken.Eleven cases of symptomatic ehrlichiosis were identified in the case-control study, 10 of which were in community A (attack rate, 330 per 100,000). Of 311 surveyed residents of community A, 12.5 percent had serologic evidence of past E. chaffeensis infection, as compared with 3.3 percent of 92 in community B (relative risk in community A as compared with community B, 3.9; 95 percent confidence interval, 1.2 to 12.2). The risk of infection was associated with tick bites, exposure to wildlife, golfing, and among golfers, retrieving lost golf balls from the rough. Persons who never used insect repellent were more likely to have had infection than persons who did. In community A, thousands of Lone Star ticks were found; in community B, only three ticks were found.The high rate of E. chaffeensis infection in community A resulted from its proximity to a wildlife reserve. When outdoor recreational activities are common and concentrations of ticks are high, outbreaks of arthropod-borne zoonoses can be anticipated.