Serologic testing for celiac disease in the United States: results of a multilaboratory comparison study

The aim of this study was to compare the efficiencies of six reference laboratories for serologic testing for celiac disease. Serum from 20 patients with untreated celiac disease and from 20 controls was thawed, divided, and distributed to each participating laboratory, which performed endomysial antibody tests. Five laboratories also performed antigliadin antibody tests. Sensitivity for endomysial antibody immunoglobulin A (IgA) varied from 57 to 90%. In all laboratories, the specificity for celiac disease was 100%. The sensitivity and specificity for both IgA and IgG antigliadin antibody varied significantly. When results from all three tests were combined in each laboratory, sensitivity was 90 to 100%. The specificity for endomysial antibody was 100% in the laboratories. Sensitivity was less than reported previously. Standardization of these tests is needed in the United States.     

Effects of OspA Vaccination on Lyme Disease Serologic Testing

This study presents the effects of OspA vaccination on two-step testing for Borrelia burgdorferi antibodies. Although vaccinees developed enzyme-linked immunosorbent assay reactivity, immunoblots did not fulfill Centers for Disease Control and Prevention criteria for positivity. Furthermore, OspA reactivity did not interfere with interpretation of immunoblots with sera from patients who developed early Lyme disease despite vaccination.     

A Novel Algorithm for the Diagnosis of Celiac Disease and a Comprehensive Review of Celiac Disease Diagnostics

There is an urgent clinical need for a better laboratory celiac disease diagnosis with both less false positive results and minimal underdetection. The aim of the present study was to evaluate the performance and diagnostic accuracy of different assays in an outpatient population setting for the diagnosis for celiac disease (CD) in order to design an optimal algorithm. We used 15 different ELISA assays to assess 47 blood samples of newly diagnosed children (positive biopsy results) and 52 samples from age- and sex-matched children with negative biopsy results for CD. Scoring criteria were established for grading the assays performance and characteristics. The combined gliadin and tTG assays exhibited the best sensitivity (100%). The addition of other assays to the CeliCheck neo-epitopes assay improved specificity so that the final algorithm had 100% sensitivity, 96.2% specificity, and 98.1% accuracy. The clinical demand for both maximal sensitivity and maximal specificity cannot be achieved with a single test. Using a combination of a sensitive assay together with specific assays improved celiac disease detection rates, with an acceptable number of false positive results. This model, however, needs to be confirmed prospectively in both children and adults.     

Serologic evidence of canine and equine ehrlichiosis in northeastern United States.

In a retrospective study, indirect fluorescent-antibody staining methods were used to detect immunoglobulins to Ehrlichia canis and Ehrlichia risticii in canine and equine sera that had originally been analyzed for antibodies to Borrelia burgdorferi. Analyses of 60 dog serum specimens collected in Connecticut and New York State during 1986 revealed antibodies to E. canis in 7 (11.7%) specimens; titration endpoints ranged from 1:40 to 1:320. Three of these dogs had anemia. Of the 187 equine serum specimens obtained in Connecticut during 1985 and analyzed by indirect fluorescent-antibody staining methods, 17 (9.1%) contained antibodies to E. risticii. Maximal antibody titers of 1:1,280 were recorded for serum specimens collected from three equids during May and July. We conclude that canine and equine ehrlichiosis coexist with Lyme borreliosis in Connecticut and the lower Hudson River Valley of New York State.     

Serologic analyses of Peromyscus leucopus, a rodent reservoir for Borrelia burgdorferi, in northeastern United States.

An enzyme-linked immunosorbent assay (ELISA) and indirect fluorescent-antibody test were used to detect antibodies to Borrelia burgdorferi, the causative agent of Lyme disease, in Peromyscus leucopus (white-footed mouse). Of the 661 mice captured in Connecticut, Rhode Island, and New York during 1980 and 1983 to 1987, 166 (25.1%) had antibodies to B. burgdorferi by ELISA. Comparative analyses of 210 serum specimens, collected in areas where Lyme disease is endemic, revealed a threefold difference in sensitivity between the ELISA (38.1% positive) and the indirect fluorescent-antibody method (12.4%). Although prevalence of seropositive P. leucopus was highest during June, elevated amounts of antibody (1:1,280 to 1:2,560) were detected in mice that harbored spirochetes during all seasons. Being reservoirs for B. burgdorferi, these rodents are suitable for monitoring spirochete infections at foci and should be included in field evaluations of control programs aimed at suppressing Lyme disease.     

Trypanosoma cruzi and Chagas' Disease in the United States

Chagas' disease is caused by the protozoan parasite Trypanosoma cruzi and causes potentially life-threatening disease of the heart and gastrointestinal tract. The southern half of the United States contains enzootic cycles of T. cruzi, involving 11 recognized triatomine vector species. The greatest vector diversity and density occur in the western United States, where woodrats are the most common reservoir; other rodents, raccoons, skunks, and coyotes are also infected with T. cruzi. In the eastern United States, the prevalence of T. cruzi is highest in raccoons, opossums, armadillos, and skunks. A total of 7 autochthonous vector-borne human infections have been reported in Texas, California, Tennessee, and Louisiana; many others are thought to go unrecognized. Nevertheless, most T. cruzi-infected individuals in the United States are immigrants from areas of endemicity in Latin America. Seven transfusion-associated and 6 organ donor-derived T. cruzi infections have been documented in the United States and Canada. As improved control of vector- and blood-borne T. cruzi transmission decreases the burden in countries where the disease is historically endemic and imported Chagas' disease is increasingly recognized outside Latin America, the United States can play an important role in addressing the altered epidemiology of Chagas' disease in the 21st century.     

Serologic Testing for Syphilis: Benefits and Challenges of a Reverse Algorithm

Syphilis is a human infection of global importance. Its diagnosis can be challenging, requiring construction of a serologic profile based on the results of at least two types of antibody tests: treponemal and nontreponemal. The traditional approach to the serodiagnosis of syphilis has been the use of a nontreponemal screening assay followed by the performance of a treponemal confirmatory test if the initial nontreponemal screening test was reactive. With the increasing availability of automated, easier-to-perform, and rapid treponemal assays, an increasing number of laboratory testing sites are adopting reverse sequence screening for the serodiagnosis of syphilis: screening with a treponemal assay first, then confirmation with a nontreponemal assay and, when necessary, discrepant resolution using another treponemal test. In addition to offering automation and increased throughput, a reverse algorithm can increase disease detection, especially in late latent and early primary stages of infection when the nontreponemal antibody test may be nonreactive. However, a disadvantage to this approach is that there can be an increase in false-positive test results. This article reviews the clinical and workflow benefits and limitations of a reverse testing algorithm and discusses current guidance available from the Centers for Disease Control and Prevention.     

The current state of adult metabolic medicine in the United States: Results of a nationwide survey

PurposePatients with inherited metabolic disorders (IMDs) now have improved health outcomes and increased survival into adulthood. There is scant evidence on managing adults with IMDs. We present an analysis of current care practices for adults with IMDs in the United States.MethodsWe created and distributed an online survey to US members of the Society of Inherited Metabolic Disorders. The survey addressed ambulatory care, acute management, and health care transition (HCT) practices of adults with IMDs.ResultsThe survey was completed by 91 providers from 73 institutions. Most adult patients with IMDs receive lifelong care from a single metabolic clinician, predominantly in pediatric clinic settings. Adults receive comprehensive ambulatory metabolic care, but fewer trainees participate compared with pediatric visits. Most acute IMD management occurs in pediatric hospitals. Clinician comfort with HCT increased the frequency of HCT planning. Overall, all respondents felt that providing specialized care to adults with IMDs is high value.ConclusionOur survey demonstrates the paucity of clinical resources dedicated to adult metabolic medicine. Care is fragmented and varies by medical system. Interest in HCT is robust but would benefit from standardized practices. Our findings reinforce the need for greater focus on adult metabolic medicine in the United States.     

Epidemiology of Group B Streptococcal Disease in the United States: Shifting Paradigms

Since its emergence 25 years ago, group B streptococcus has become recognized as a cause of serious illness in newborns, pregnant women, and adults with chronic medical conditions. Heavy colonization of the genital tract with group B streptococcus also increases the risk that a woman will deliver a preterm low-birthweight infant. Early-onset infections (occurring at <7 days of age) are associated with much lower fatality than when they were first described, and their incidence is finally decreasing as the use of preventive antibiotics during childbirth increases among women at risk. New serotypes of group B streptococcus have emerged as important pathogens in adults and newborns. Clinical and laboratory practices—in obstetrics, pediatrics, and clinical microbiology—have an impact on disease and/or its prevention, and protocols established at the institutional level appear to be critical tools for the reduction of perinatal disease due to group B streptococcus. Since intrapartum antibiotics will prevent at best only a portion of the full burden of group B streptococcal disease, critical developments in vaccine evaluation, including study of polysaccharide-protein conjugate vaccines, offer the potential for enhanced prevention in the relatively near future.     

Serologic Evidence of Infection with Ehrlichia spp. in Wild Rodents (Muridae: Sigmodontinae) in the United States

Rodent (Muridae: Sigmodontinae) blood and sera collected from 14 states were tested for seroreactivity to a cultured isolate of the human granulocytic ehrlichiosis (HGE) agent by using an indirect immunofluorescence assay. Of the 1,240 samples tested, 136 (11%) were found to be reactive at titers of ≥32. Rodents with HGE agent-specific antibodies were found in New York (23% of 491 samples; geometric mean endpoint titer [GMT] = 441), Connecticut (11% of 100 samples; GMT = 481), California (9% of 32 samples; GMT = 323), Colorado (2% of 212 samples; GMT = 256), Florida (7% of 27 samples; GMT = 362), Maryland (7% of 15 samples; titer = 64), New Jersey (4% of 76 samples; titer = 256), and Wisconsin (13% of 8 samples; titer = 128). Samples from Georgia (n = 16), Illinois (n = 27), Nevada (n = 27), North Carolina (n = 52), Ohio (n = 57), and Utah (n = 100) were not reactive. The earliest seroreactive sample was from a Peromyscus leucopus mouse collected in June 1986 in Connecticut, and the majority of the seroreactive samples (68%) were from this species. Samples from other Peromyscus species (P. boylii, P. maniculatus, and P. gossypinus) were also found to be reactive, with a GMT for the genus of 410. Several species of Neotoma woodrats (N. fuscipes, N. lepida, N. albigula, and N. mexicana) from California and Colorado had antibodies that reacted with the HGE agent (genus GMT = 194), suggesting that enzootic cycles of Ehrlichia spp. exist outside of the areas of confirmed human disease. Attempts to amplify and detect ehrlichial DNA from the limited tissues available (n = 40 animals) were unsuccessful. Further studies are needed to determine the identity of the organisms inducing antibody production in these rodent species and to elucidate the epidemiology and public health importance of these agents.     

Multilaboratory Evaluation of In Vitro Antifungal Susceptibility Testing of Dermatophytes for ME1111

ME1111 is a novel small molecule antifungal agent under development for the topical treatment of onychomycosis. Standardization of the susceptibility testing method for this candidate antifungal is needed. Toward this end, 8 independent laboratories determined the interlaboratory reproducibility of ME1111 susceptibility testing. In addition, we subsequently identified 2 strains as quality control (QC) isolates for the method. In the reproducibility study, 5 blinded clinical strains each of Trichophyton rubrum, Trichophyton mentagrophytes, and Epidermophyton floccosum were tested, while the QC study tested 6 blinded T. rubrum or T. mentagrophytes ATCC strains. Testing was performed in frozen microtiter panels according to the Clinical and Laboratory Standards Institute (CLSI) M38-A2 methodology. In the reproducibility study, 9 of 15 clinical strains showed interlaboratory agreement of >90% at the 80% inhibition endpoint, with a range of agreement of 76.2% to 100%. In the QC study, 4 of the 6 ATCC strains showed interlaboratory agreement of >90%. ME1111 demonstrated excellent interlaboratory agreement when tested against dermatophytes. Based on this data, the CLSI Subcommittee on Antifungal Susceptibility Tests approved the susceptibility testing of ME1111 against dermatophytes according to M38-A2 methodology, which stipulates RPMI 1640 as the test medium, an inoculum size of 1 to 3 × 10³ CFU/ml, and an incubation time and temperature of 96 h at 35°C. The MIC endpoint should be 80% inhibition compared with the growth control. T. rubrum ATCC MYA-4438 and T. mentagrophytes ATCC 28185 were selected as QC isolates, with an acceptable range of 0.12 to 1 μg/ml for the two strains.     

Salmonella enterica Serotype Dublin Infection: an Emerging Infectious Disease for the Northeastern United States

Salmonella enterica subspecies enterica serotype Dublin (S. enterica Dublin) emerged for the first time in New York, Pennsylvania, and Ohio in 1988. Since that time this host-adapted serotype has spread throughout the veal- and dairy beef-raising operations in the region; very few dairy farms have experienced clinical S. enterica Dublin infections. This study details the epidemiology of the outbreaks in cattle. During the period 1988 through 1995, nine New York and four Pennsylvania counties have been affected; 13 different locations were involved in New York, and 10 were involved in Pennsylvania. The morbidity and mortality and seasonal distribution of outbreaks, which totaled 35, is described. The antimicrobial susceptibility pattern of isolates revealed that many of the strains were resistant to a number of commonly used drugs. Clinical case details and pathology information are provided, with a caution to clinicians and microbiologists presented with suspect animals, i.e., most cases occurred in older calves, which is atypical for salmonellosis for this region (calves were 8 or more weeks old) and presented as pneumonia and septicemia rather than the primarily diarrheal syndrome that is more typically recognized for the region. The epidemiology of cases is analyzed through cluster analysis of bacterial isolates and their fatty acid methyl ester profiles; at least six clones appeared in the region during the study period. Results of the epidemiology analysis are used to support a hypothesis regarding the source of S. enterica Dublin for the region and its manner of dissemination.     

Celiac Disease: Presentation of 109 Children

Purpose

The clinical features of patients with celiac disease (CD) are variable. In the present study, clinical and laboratory features of 109 patients with CD were retrospectively evaluated.

Materials and Methods

In all cases, diagnosis of CD was made by European Society for Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN) criteria and clinical and laboratory findings, including hematological and biochemical analyses, immunoglobulin levels, autoantibodies [antinucler antibody (ANA), antidouble stranded DNA (dsDNA), antimitochondrial antibody (AMA), anti-smooth muscle antibody (ASMA), liver kidney antibody (LKM-1), anti thyroid peroxidase (TPO), anti thyroglobulin (Tg)], bone mineral density (BMD), and electroencephalogram were evaluated. The type of CD was recorded.

Results

Of 109 patients with CD, 66 (60.6%) were classical type, 41 (37.6%) were atypical type and 2 (1.8%) were silent type. The mean age was 8.81 ± 4.63 years and the most common symptom was diarrhea (53.2%) followed by failure to thrive, short stature, and abdominal pain. Paleness (40.4%), underweight (34.8%), and short stature (31.2%) were the most common findings. Iron deficinecy anemia (81.6%), zinc deficiency (64.1%), prolonged prothrombin time (35.8%), and elevated transaminase levels (24.7%) were the most common laboratory findings. Eight percent of patients had at least 1 autoantibody, and 28 of 52 patients had low BMD. Four of 38 patients had abnormalty in electroencephalograms. The prevalance of selective immunoglobulin (Ig) A deficiency was 9.1%. Histocompatibility antigen HLA-DQ and/or DQ8 genotypes were found in 91% of patients. Abdominal distention, iron deficiency, prolonged prothrombine time, hypoalbuminemia, and elevated transaminase levels were more significantly frequent in the classical type than atypical type (p < 0.005).

Conclusion

Although classical CD was seen in most patients in the present study, clinical variability of the condition should be kept in mind.     

中美两种2型糖尿病肾病诊断标准中疾病进展及预后因素对比

目的 通过对美国肾脏病基金会肾脏病预后质量倡议（NKF K/DOQI）标准及中华医学会糖尿病学分会微血管并发症学组的标准所描述的2型糖尿病肾病疾病进展及预后因素进行对比,评估两种标准的临床应用价值。方法 选取2016年4月~2017年4月于佛山市第二人民医院就诊的2型糖尿病患者共280例作研究对象,其中符合NKF K/DOQI标准的2型糖尿病肾病患者70例,符合中华医学会标准者80例。记录两种标准2型糖尿病肾病患者的肾小球滤过率,两组患者接受1年回访后对上述指标进行复查,统计两种标准患者的肾功能进展性下降的比例并进行对比。使用Spearson法分析eGFR下降幅度与各可能危险因素的相关性,使用Logistic回归模型分析随访后eGFR下降与各可能危险因素的相关性。结果 中华医学会标准诊断2型糖尿病患者的糖尿病肾病患病率为:28.57%（80/280）;NKF K/DOQI标准诊断2型糖尿病患者的糖尿病肾病患病率为25.00%（70/280）;按中华医学会标准,正常白蛋白尿的2型糖尿病肾病患者占2型糖尿病肾病患者的12.50%（10/80）;两种标准下,糖尿病肾病患者出现eGFR降低≥4%/年的比例均高于非糖尿病肾病者,中华医学会标准组为:20.00% vs 9.00%（P＜0.05）;NKF K/DOQI标准组为:17.14% vs 6.67%（P＜0.05）;两种标准下糖尿病肾病与非糖尿病肾病在eGFR降低＜4%及eGFR无下降的患者比较,差异无统计学意义（P＞0.05）;Logistic回归分析中,校正年龄、血糖、病程等危险因素后,中华医学会标准下糖尿病病程≥10年、HbA1C、基线eGFR与eGFR进展性下降存在显著相关性;NKF K/DOQI标准下糖尿病病程≥10年、高血压、HbA1C、基线eGFR、糖尿病视网膜病变与eGFR进展性下降存在显著相关性。结论 两种标准诊断的糖尿病肾病患者肾功能进展性下降程度均高于非糖尿病肾病患者,预测两种标准糖尿病肾病发生肾功能进展性下降的基线预后因素相似,本研究对中华医学会标准将正常白蛋白尿但eGFR下降的临床亚型归入2型糖尿病肾病诊断范畴的建议提供了流行病学的间接证据。     

The Past,Present, and (Possible) Future of Serologic Testing for Lyme Disease

Lyme disease prevails as the most commonly transmitted tick-borne infection in the United States, and serologic evaluation for antibodies to Borrelia burgdorferi remains the recommended modality for diagnosis. This review presents a brief historical perspective on the evolution of serologic assays for Lyme disease and provides a summary of the performance characteristics for the currently recommended two-tiered testing algorithm (TTTA). Additionally, a recently proposed alternative to the traditional TTTA is discussed, and novel methodologies, including immuno-PCR and metabolic profiling for Lyme disease, are outlined.     

Performance of Serology Assays for Diagnosing Celiac Disease in a Clinical Setting

Diagnosis of celiac disease frequently depends upon serology assays. We set out to prospectively assess the diagnostic value of five serology tests: an enzyme-linked immunosorbent assay (ELISA) for tissue transglutaminase (tTG)-immunoglobulin A (IgA) and tTG-IgG, a chemiluminescence assay for tTG-IgA, an ELISA for deamidated gliadin peptide (DGP) IgG and IgA screening, and detection of endomysial antibodies (Abs) by indirect immunofluorescence. One hundred sixteen children at high risk for developing celiac disease were evaluated clinically and underwent small bowel biopsies and blood serology tests. We examined differences between younger and older children in terms of clinical presentation, test performance, and the ability of high Ab levels to correctly predict diagnosis of celiac disease. Celiac disease was diagnosed for 85 (73%) children. No significant clinical differences were observed between the biopsy-positive and biopsy-negative groups. Children ≤3 years of age revealed higher concentrations of tTG-IgA and DGP Abs than children >3 years old (P = 0.017 and 0.007, respectively). High Ab concentrations were predictive of villous atrophies, with sensitivities ranging from 92.8% to 97.9%, depending on the assay and the cutoff points applied. Sensitivities, specificities, positive predictive values, and negative predictive values varied among assays and improved after correction for best cutoff points. Assay specificities obtained in the clinical setting were lower than expected. The new tTG-IgA chemiluminescence assay demonstrated high throughput but low specificity (74.2%). The tTG-IgA ELISA exhibited the highest test efficiency, and the tTG-IgA chemiluminescence assay was suitable for large-scale screening, with reduced specificity. High concentrations of celiac disease-specific Abs bring into question the need for performance of biopsies on children at high risk.Celiac disease (CD) is a common autoimmune enteropathy that occurs in genetically predisposed children and adults upon ingestion of gluten or related proteins (19). The diverse presentation of CD includes classical clinical symptoms, such as diarrhea, weight loss, failure to thrive, malabsorption, and anemia, and atypical manifestations, such as nonspecific abdominal pain, esophageal reflux, osteoporosis, hypertransaminasemia, and neurological symptoms (15, 25). Population studies have shown that the incidences of CD in Europe and North America are 0.5 to 1% (10). Even though the rate of diagnosis has increased in recent years, according to the accepted iceberg concept (11), the majority of affected individuals are still undiagnosed (10, 18).According to the latest consensus report on CD, small bowel biopsies are considered the gold standard and are mandatory for diagnosis (15). Obtaining a biopsy specimen is an invasive procedure and at times may miss patchy mucosal changes. Poor orientation of the removed tissue may lead to difficulties in interpretation. On the other hand, serology testing for CD-specific antibodies (Abs) is easy to perform and a wide range of commercial kits are now available. The serology tests are sensitive and specific and are becoming the obligatory tool for correctly referring patients for biopsies. Immunoglobulin A (IgA) against the tissue transglutaminase (tTG) antigen is accepted as the best serology screening tool performed by the enzyme-linked immunosorbent assay (ELISA) method (15). Recently, a new human recombinant tTG-IgA chemiluminescence assay was developed for use with the Immulite 2000 analyzer. This platform enables large-scale testing at a high throughput, an advantage which should be taken into account due to the increasing requests for serology testing. In many clinical laboratories, the fluorescence endomysial Ab (EMA) assay is used for confirming the presence of tTG-IgA. The EMA assay is known for its high sensitivity and specificity for diagnosing CD but requires much technologist labor and yet suffers from interobserver variability in interpretation. Abs to deamidated gliadin peptides (DGP) were shown to be of diagnostic value, and DGP Ab kits are being extensively evaluated (2, 28, 29, 32, 36). A DGP assay recognizing both IgA and IgG Abs, known as the DGP (IgA+IgG) screen, is intended for detecting both IgA-deficient and IgA-sufficient CD patients. Thus, the need for measuring total IgA for all tested subjects is eliminated. IgA deficiency affects approximately 1/500 of the general population and is a 10-fold-increased risk factor for CD (8). Performance of the DGP (IgA+IgG) screen could reduce test costs by eliminating the need for IgA screening.tTG-IgA Ab titer was shown to correlate well with severity of biopsy result in adults and pediatric populations (14, 33). This positive correlation has raised the possibility of avoiding small bowel biopsies, when tTG-IgA Ab concentrations are especially high, for diagnosing high-risk populations (3, 13). This concept is not thoroughly studied with the various tTG-IgA commercial kits or other CD Ab specificities. The majority of studies regarding the diagnostic value of CD serology were conducted in research settings. A few publications raised the possibility that serology assays may be less accurate when used in clinical settings (1, 21). We therefore examined a group of children presenting clinical suspicion for developing CD in our community clinical setting. The high prevalence of biopsy-proven CD children in this population enabled us to examine the diagnostic value of several serology kits by comparing the results for two age groups. We also calculated the correlations between Ab titer and severity of biopsy result and assessed the possibility that high Ab titers have predictive value for biopsy results.     

Serologic Testing for Human Granulocytic Ehrlichiosis at a National Referral Center

An indirect immunofluorescence assay (IFA) was used to identify patients with antibodies reactive to the human granulocytic ehrlichiosis (HGE) agent. Serum samples collected from clinically ill individuals were submitted to the Centers for Disease Control and Prevention by physicians via state health departments from throughout the United States and tested against a panel of ehrlichial and rickettsial pathogens. Antibodies reactive to the HGE agent were detected in 142 (8.9%) of 1,602 individuals tested. There were 19 confirmed and 59 probable (n = 78) cases of HGE as defined by seroconversion or a fourfold or higher titer to the HGE agent than to the Ehrlichia chaffeensis antigens. The average age of patients with HGE was 57 years, and males accounted for 53 (68%) of the patients. Cases of HGE occurred in 21 states; 47 (60%) of the cases occurred in Connecticut (n = 14), New York (n = 18), and Wisconsin (n = 15). Onset of HGE was identified from April through December, with cases peaking in June and July. The earliest confirmed cases of HGE occurred in 1987 in Wisconsin and 1988 in Florida. No fatalities were reported among the 78 patients with confirmed or probable HGE. Reactivity to the HGE agent and to either Coxiella burnetii, Rickettsia rickettsii, or Rickettsia typhi was infrequent; however, 74 (52%) of the 142 individuals who were positive for HGE had at least one serum sample that also reacted to the E. chaffeensis antigen. Thirty-four persons with confirmed or probable human monocytic ehrlichiosis due to E. chaffeensis also had antibodies to the HGE agent in at least one serum sample. The specific etiologic agent for 30 patients was not ascribed because of similarity of titers to both ehrlichial antigens. The use of both antigens may be required to correctly diagnose most cases of human ehrlichiosis, especially in geographic regions where both the HGE agent and E. chaffeensis occur.