Tick bite as a risk factor for alpha-gal-specific immunoglobulin E antibodies and development of alpha-gal syndrome.

BACKGROUND: The disaccharide galactose-α-1,3-galactose (alpha-gal) is expressed in mammals other than humans, apes, and old-world monkeys. In humans, elevated immunoglobulin E (IgE) antibodies specific for alpha-gal can result in allergic hypersensitivity known as alpha-gal syndrome (AGS). Case reports and series suggest that tick bites can induce alpha-gal-specific IgE (sIgE) antibodies. OBJECTIVE: To evaluate tick exposure as a risk factor for AGS and elevated alpha-gal sIgE level. METHODS: We conducted a case-control study comparing patients with AGS from a North Carolina allergy clinic with controls who were patients at a nearby internal medicine clinic. Cases and controls were administered a questionnaire to obtain information about demographics, home environment, outdoor activities, and recollection of tick bite. Serum samples taken at the time of enrollment were tested for total IgE, alpha-gal sIgE, and antibodies to other tick-borne pathogens. RESULTS: The patients with AGS were more likely to recall finding a tick on themselves (odds ratio [OR], 11.20; 95% confidence interval [CI], 4.97-25.15), live near wooded forest (OR, 2.27; 95% CI, 0.92-5.55), and spend 17 or more hours per week outdoors in wooded areas (OR, 5.58; 95% CI, 2.56-12.19). The patients with AGS were also more likely to report 4 or more tick bites (OR, 33.05; 95% CI, 9.92-155.12) and reactions at the site of tick bites (OR, 7.93; 95% CI, 3.74-16.80). Furthermore, elevated alpha-gal sIgE level was observed in 33% of the controls and was associated with tick exposure in the controls (OR, 4.25; 95% CI, 2.21-8.18). CONCLUSION: The results define tick bite as a risk factor for AGS and elevated alpha-gal sIgE level.

Expertise and information: an epistemic logic perspective.

In this paper we present a modal logic framework to reason about the expertise of information sources. A source is considered an expert on a proposition φ if they are able to correctly refute φ in any possible world where φ is false. Closely connected with expertise is a notion of soundness of information: φ is said to be "sound" if it is true up to lack of expertise of the source. That is, any statement logically weaker than φ on which the source has expertise must in fact be true. This is relevant for modelling situations in which sources make claims beyond their domain of expertise. Particular attention is paid to the connection between expertise and knowledge: we show that expertise and soundness admit precise interpretations in terms of S4 and S5 epistemic logic, under certain conditions. We go on to extend the framework to multiple sources, defining two notions of collective expertise. These also have epistemic interpretations via distributed and common knowledge from multi-agent epistemic logic. On the technical side, we give several sound and complete axiomatisations of various classes of expertise models.

Antibody Titers Reactive With Rickettsia rickettsii in Blood Donors and Implications for Surveillance of Spotted Fever Rickettsiosis in the United States.

BACKGROUND: Since 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. METHODS: Donor 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. RESULTS: Of 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. CONCLUSIONS: These 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.

Rickettsia parkeri Rickettsiosis, Arizona, USA.

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.

A non-comparative evaluation of a chitosan gelling fibre.

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.

A confirmed Ehrlichia ewingii infection likely acquired through platelet transfusion.

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.

Acute febrile illness among outpatients seeking health care in Bangladeshi hospitals prior to the COVID-19 pandemic.

Understanding the distribution of pathogens causing acute febrile illness (AFI) is important for clinical management of patients in resource-poor settings. We evaluated the proportion of AFI caused by specific pathogens among outpatients in Bangladesh. During May 2019-March 2020, physicians screened patients aged ≥2 years in outpatient departments of four tertiary level public hospitals. We randomly enrolled patients having measured fever (≥100.4°F) during assessment with onset within the past 14 days. Blood and urine samples were tested at icddr,b through rapid diagnostic tests, bacterial culture, and polymerase chain reaction (PCR). Acute and convalescent samples were sent to the Centers for Disease Control and Prevention (USA) for Rickettsia and Orientia (R/O) and Leptospira tests. Among 690 patients, 69 (10%) had enteric fever (Salmonella enterica serotype Typhi orSalmonella enterica serotype Paratyphi), 51 (7.4%) Escherichia coli, and 28 (4.1%) dengue detected. Of the 441 patients tested for R/O, 39 (8.8%) had rickettsioses. We found 7 (2%) Leptospira cases among the 403 AFI patients tested. Nine patients (1%) were hospitalized, and none died. The highest proportion of enteric fever (15%, 36/231) and rickettsioses (14%, 25/182) was in Rajshahi. Dhaka had the most dengue cases (68%, 19/28). R/O affected older children and young adults (IQR 8-23 years) and was detected more frequently in the 21-25 years age-group (17%, 12/70). R/O was more likely to be found in patients in Rajshahi region than in Sylhet (aOR 2.49, 95% CI 0.85-7.32) between July and December (aOR 2.01, 1.01-5.23), and who had a history of recent animal entry inside their house than not (aOR 2.0, 0.93-4.3). Gram-negative Enterobacteriaceae were the most common bacterial infections, and dengue was the most common viral infection among AFI patients in Bangladeshi hospitals, though there was geographic variability. These results can help guide empiric outpatient AFI management.

Brill-Zinsser disease in a patient following infection with sylvatic epidemic typhus associated with flying squirrels.

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.

Expanding Recognition of Rickettsia parkeri Rickettsiosis in Southern Arizona, 2016-2017.

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.

Distinguishing patients with laboratory-confirmed chikungunya from dengue and other acute febrile illnesses, Puerto Rico, 2012-2015.

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 <3 DPO. Regardless of timing of presentation, significant positive predictors for chikungunya versus other AFI were: joint pain, muscle, bone or back pain, skin rash, and red conjunctiva; with dengue as the comparator, red swollen joints (arthritis), joint pain, skin rash, any bleeding, and irritability were predictors. Chikungunya cases were less likely than AFI and dengue to present with thrombocytopenia, signs of poor circulation, diarrhea, headache, and cough. Among participants presenting <3 DPO, predictors for chikungunya versus other AFI included: joint pain, skin rash, and muscle, bone or back pain, and absence of thrombocytopenia, poor circulation and respiratory or gastrointestinal symptoms; when the comparator was dengue, joint pain and arthritis, and absence of thrombocytopenia, leukopenia, and nausea were early predictors. Among all groups presenting 3-5 DPO, pruritic skin became a predictor for chikungunya, joint, muscle, bone or back pain were no longer predictive, while arthritis became predictive in all age-groups. Absence of thrombocytopenia was a significant predictor regardless of DPO or comparison group. This study identified robust clinical indicators such as joint pain, skin rash and absence of thrombocytopenia that can allow early identification of and accurate differentiation between patients with chikungunya and other common causes of AFI.

Rocky Mountain spotted fever from an unexpected tick vector in Arizona.

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.

Q fever in an American tourist returned from Australia.

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.

Clinical and epidemiologic characteristics of dengue and other etiologic agents among patients with acute febrile illness, Puerto Rico, 2012-2015.

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 <3 DPO included leukopenia, thrombocytopenia, headache, eye pain, nausea, and dizziness, while negative predictors were irritability and rhinorrhea. Predictors of dengue in participants presenting 3-5 DPO were leukopenia, thrombocytopenia, facial/neck erythema, nausea, eye pain, signs of poor circulation, and diarrhea; presence of rhinorrhea, cough, and red conjunctiva predicted non-dengue AFI. By enrolling febrile patients at clinical presentation, we identified unbiased predictors of laboratory-positive dengue as compared to other common causes of AFI. These findings can be used to assist in early identification of dengue patients, as well as direct anticipatory guidance and timely initiation of correct clinical management.

Coxiella burnetii Infection in a Community Operating a Large-Scale Cow and Goat Dairy, Missouri, 2013.

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.

Rickettsialpox in New York City: a persistent urban zoonosis.

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.

Imported spotted fever rickettsioses in United States travelers returning from Africa: a summary of cases confirmed by laboratory testing at the Centers for Disease Control and Prevention, 1999-2002.

The increasing popularity of foreign travel and ecotourism places travelers at increased risk for certain tick-borne diseases. From 1999 through 2002, 31 cases of imported spotted fever-group rickettsioses (SFGR) in United States residents reporting travel to Africa were confirmed by laboratory testing at the Centers for Disease Control and Prevention. Nineteen patients (61%) reported visiting South Africa prior to illness onset. Most patients reported fever and one or more eschars; rash was reported for only 26% of the patients. Twelve patients had an initial non-reactive acute-phase serum sample obtained a median of three days after illness onset, and were confirmed by testing a second convalescent-phase serum sample obtained a median of 32 days after illness onset. Five patients were confirmed positive through immunohistochemical staining of skin biopsies, including three patients with acute-phase serum samples that tested negative for SFGR. This study emphasizes the importance of evaluating convalescent-phase serum specimens 28 days or more after illness onset or examining skin biopsies by immunohistochemical staining during early infection to confirm a diagnosis of imported SFGR.

Increased detection of rickettsialpox in a New York City hospital following the anthrax outbreak of 2001: use of immunohistochemistry for the rapid confirmation of cases in an era of bioterrorism.

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 (> or =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.

Pseudoepidemic of Q fever at an animal research facility.

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.

Rickettsia parkeri rickettsiosis in different ecological regions of Argentina and its association with Amblyomma tigrinum as a potential vector.

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.

Inadequacy of IgM antibody tests for diagnosis of Rocky Mountain Spotted Fever.

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.