Clinical Significance and Characterization of Streptococcus tigurinus Isolates in an Adult Population.

Streptococcus tigurinus is a newly described member of the Streptococcus mitis group. Due to the difficulty in distinguishing viridans group streptococci (VGS) by phenotype, analysis of 16S rRNA sequences is necessary for the accurate identification of most species. Through a laboratory policy of analyzing all clinically significant isolates from the VGS group by16S rRNA gene sequencing, we identified 14 S. tigurinus isolates from 11 patients. The Vitek 2 system most commonly gave an excellent rating to an incorrect identification (e.g., Streptococcus mitis), as did matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) (e.g., Streptococcus oralis). S. tigurinus strains were recovered from numerous body sites, including the blood, peritoneal fluid, bone, synovial fluid, a perianal abscess, and an arm wound. Retrospective chart review indicated that most isolates were clinically significant, with bacteremia (n = 5), soft tissue infections (n = 3) osteomyelitis (n = 2), infected joint prosthesis (n = 2), and peritonitis (n = 2) being the most common, thus expanding the spectrum of disease associated with S. tigurinus.

Genotypic and phenotypic characterization and clinical significance of 'Haemophilus quentini' isolated from the urinary tract of adult men.

'Haemophilus quentini' has been proposed as the name for a distinct and homogeneous Haemophilus genospecies associated with urogenital tract and neonatal-related infections. Reports of 'H. quentini' isolation from adult men are rare and the disease potential in this population is unknown. We report six cases where 'H. quentini' was isolated from the genito-urinary tract in males. The isolation of 'H. quentini' during routine urine and urethral culture in adult men may aid in the determination of unresolved urethritis and possible urinary tract infections.

16S ribosomal DNA sequence analysis distinguishes biotypes of Streptococcus bovis: Streptococcus bovis Biotype II/2 is a separate genospecies and the predominant clinical isolate in adult males.

We characterized 22 human clinical strains of Streptococcus bovis by genotypic (16S rRNA gene sequence analysis [MicroSeq]; Applied Biosystems, Foster City, Calif.) and phenotypic (API 20 Strep and Rapid ID32 Strep systems (bioMerieux Vitek, Hazelton, Mo.) methods. The strains, isolated from blood, cerebrospinal fluid (CSF), and urine, formed two distinct 16S ribosomal DNA sequence clusters. Three strains which were associated with endocarditis urinary tract infection (UTI), and sepsis clustered with the S. bovis type strain ATCC 33317 (cluster 1); other closely related type strains were S. equinus and S. infantarius. Nineteen strains clustered at a distance of about 2.5% dissimilarity to the S. bovis type strain (cluster 2) and were associated with central nervous system (CNS) disease in addition to endocarditis, UTI, and sepsis. All strains were distinct from S. gallolyticus. Within cluster 2, a single strain grouped with ATCC strain 43143 (cluster 2a) and may be phenotypically distinct. All the other strains formed a second subgroup (cluster 2b) that was biochemically similar to S. bovis biotype II/2 (mannitol negative and beta galactosidase, alpha galactosidase, beta glucuronidase, and trehalose positive). The API 20 Strep system identified isolates of cluster 2b as S. bovis biotype II/2, those of cluster 1 as S. bovis biotype II/1, and that of cluster 2a as S. bovis biotype I. There was an excellent correlation of biotype and genotype: S. bovis biotype II/2 isolates form a separate genospecies distinct from the S. bovis, S. gallolyticus, and S. infantarius type strains and are the most common isolates in adult males.

Antibiotic susceptibilities of genetically characterized Streptococcus milleri group strains.

Previous studies of the antibiotic susceptibility of Streptococcus milleri group organisms have distinguished among species by using phenotypic techniques. Using 44 isolates that were speciated by 16S rRNA gene sequencing, we studied the MICs and minimum bactericidal concentrations of penicillin, ampicillin, ceftriaxone, and clindamycin for Streptococcus intermedius, Streptococcus constellatus, and Streptococcus anginosus. None of the organisms was resistant to beta-lactam antibiotics, although a few isolates were intermediately resistant; one strain of S. anginosus was tolerant to ampicillin, and another was tolerant to ceftriaxone. Six isolates were resistant to clindamycin, with representation from each of the three species. Relatively small differences in antibiotic susceptibilities among species of the S. milleri group show that speciation is unlikely to be important in selecting an antibiotic to treat infection caused by one of these isolates.

Evaluation of PCR-based methods for discrimination of Francisella species and subspecies and development of a specific PCR that distinguishes the two major subspecies of Francisella tularensis.

Previous studies have demonstrated that the four subspecies of the human pathogen Francisella tularensis, despite showing marked variations in their virulence for mammals and originating from different regions in the Northern Hemisphere, display a very close phylogenetic relationship. This property has hampered the development of generally applicable typing methods. To overcome this problem, we evaluated the use of PCR for discrimination of the subspecies using various forms of long arbitrary primers or primers specific for repetitive extragenic palindromic sequences (REP) or enterobacterial repetitive intragenic consensus (ERIC) sequences. Patterns generated by use of REP, ERIC, or long arbitrary primers allowed differentiation at the species level and of the four subspecies of F. tularensis. With each of these three methods, similar or identical clustering of strains was found, and groups of strains of different geographical origins or differing in virulence showed distinct patterns. The discriminatory indices of the methods varied from 0.57 to 0.65; thus, the patterns were not sufficiently discriminatory to distinguish individual strains. The sequence of a fragment generated by amplification with an arbitrary primer was determined, and a region showing interstrain heterogeneity was identified. Specific primers were designed, and a PCR was developed that distinguished strains of F. tularensis subsp. holarctica from strains of other F. tularensis subspecies, including strains of the highly virulent F. tularensis subsp. tularensis. Notably, one European isolate showed the genetic pattern typical of the highly virulent F. tularensis subsp. tularensis, generally believed to exist only in North America. It is proposed that a combination of the specific PCR together with one method generating subspecies-specific patterns is suitable as a rapid and relatively simple strategy for discrimination of Francisella species and subspecies.

Multilaboratory validation of rapid spot tests for identification of Escherichia coli.

To validate the accuracy of rapid tests for identification of Escherichia coli, five laboratories sequentially collected 1,064 fresh, clinically significant strains with core criteria of indole-positive, oxidase-negative, nonspreading organisms on sheep blood agar plates (BAP), having typical gram-negative rod plate morphology, defined as good growth on gram-negative rod-selective media. An algorithm using beta-hemolysis on BAP, lactose reaction on eosin-methylene blue or MacConkey agar, L-pyrrolidonyl-beta-naphthylamide (PYR), and 4-methylumbelliferyl-beta-D-glucuronide (MUG) was evaluated. Identifications using the algorithm were compared to those obtained using commercial kit system identifications. One thousand strains were E. coli and 64 were not E. coli by kit identifications, which were supplemented with conventional biochemical testing of low probability profiles. Of the 1,064 isolates meeting the core criteria, 294 were beta-hemolytic and did not require further testing to be identified as E. coli. None of the 64 non-E. coli strains were hemolytic, although other indole-positive, lactose-negative species were found to be hemolytic when further strains were examined in a follow-up study. Of the remaining strains, 628 were identified as E. coli by a lactose-positive and PYR-negative reaction. For nonhemolytic, lactose-negative E. coli, PYR was not helpful, but a positive MUG reaction identified 65 of 78 isolates as E. coli. The remaining 13 E. coli strains required kit identifications. This scheme for E. coli identification misidentified three non-E. coli strains as E. coli, for an error rate of 0.3%. A total of 13 kit identifications, 657 PYR tests, and 113 MUG tests were needed to identify 1,000 E. coli strains with the algorithm. The use of this rapid system saves laboratory resources, provides timely identifications, and yields rare misidentifications.

Aerococcus urinae in urinary tract infections.

Aerococcus urinae is a rarely reported pathogen, possibly due to difficulties in the identification of the organism. A. urinae is a gram-positive coccus that grows in pairs and clusters, produces alpha-hemolysis on blood agar, and is negative for catalase and pyrrolidonyl aminopeptidase. Some of these characteristics and its being absent from the databases of most commercial identification systems could allow A. urinae to be misidentified as a streptococcus, enterococcus, or staphylococcus. We report two cases of urinary tract infection (UTI) caused by A. urinae and characterize these isolates by morphology, biochemical testing, whole-cell fatty acid analysis, 16S rRNA gene sequencing, and antibiotic susceptibilities. Most patients infected with A. urinae are elderly males with predisposing conditions who present initially with UTI. Because A. urinae is resistant to sulfonamides, treatment could be inappropriate, with infections resulting in serious complications, including death. It is important for the clinician and the microbiologist to consider A. urinae a potential pathogen and proceed with thorough microbiological identification.

Assessment of morphology for rapid presumptive identification of Mycobacterium tuberculosis and Mycobacterium kansasii.

Mycobacterium tuberculosis often exhibits serpentine cording when grown in liquid medium, whereas Mycobacterium kansasii can be larger and cross-barred. We assessed the use of these morphologic characteristics as a cost-effective method for rapid presumptive identification of isolates from BACTEC bottles. Without specific training, using the Kinyoun acid-fast stain, definitive cording was found in 237 of 373 specimens positive for M. tuberculosis (64%) and cross-barring was recognized within 63 of 76 (83%) of the specimens positive for M. kansasii, giving sensitivities specificities, positive predictive values, and negative predictive values of 63.5, 96, 92, and 79%, respectively, for M. tuberculosis and 83, 95, 59, and 98%, respectively, for M. kansasii. With training and experience, these results improved to 74.5, 98, 96, and 84% and 93, 98, 79, and 98%, respectively. The major improvements were in distinguishing the pseudocording, or loose aggregation of Mycobacterium avium complex from M. tuberculosis and the long beaded forms of Mycobacterium gordonae from M. kansasii. Mycobacterium asiaticum and Mycobacterium szulgai, which rarely occur, are genetically related to M. kansasii and morphologically difficult to distinguish. In defined circumstances, serpentine cording and cross-barring can be used for rapid presumptive identification of M. tuberculosis and M. kansasii, respectively, and as guides for initial probe selection to reduce costs.

Potential errors in recognition of Erysipelothrix rhusiopathiae.

Here we describe four isolations of Erysipelothrix rhusiopathiae associated with polyarthralgia and renal failure, septic arthritis, classic erysipeloid, and peritonitis. Although the biochemical identification was straightforward in each case, recognition presented a challenge to the clinical microbiologist, since in three cases E. rhusiopathiae was not initially considered due to unusual clinical presentations, in two cases the significance might not have been appreciated because growth was in broth only, and in one case the infection was thought to be polymicrobic. Because the Gram stain can be confusing, abbreviated identification schemes that do not include testing for H(2)S production could allow E. rhusiopathiae isolates to be misidentified as Lactobacillus spp. or Enterococcus spp. in atypical infections.

The role of clinical suspicion in evaluating a new diagnostic test for active tuberculosis: results of a multicenter prospective trial.

CONTEXT: In laboratory trials, nucleic acid amplification tests for the diagnosis of tuberculosis (TB) are more accurate than acid-fast bacilli (AFB) smear microscopy and are faster than culture. The impact of these tests on clinical diagnosis is not known. OBJECTIVE: To assess the performance of a nucleic acid amplification test, the enhanced Mycobacterium tuberculosis Direct (E-MTD) test, against a uniform clinical standard stratified by level of clinical suspicion. DESIGN: Prospective multicenter trial conducted between February and December 1996, documenting the clinical suspicion of TB at enrollment and using final comprehensive diagnosis as the criterion standard. SETTING: Six urban medical centers and 1 public health TB clinic. PATIENTS: A total of 338 patients with symptoms and signs consistent with active pulmonary TB and complete clinical diagnosis were stratified by the clinical investigators to be at low (< or =25%), intermediate (26%-75%), or high (>75%) relative risk of having TB. MAIN OUTCOME MEASURES: Sensitivity, specificity, and positive and negative predictive values of the E-MTD test in clinical suspicion of groups with low (n = 224); intermediate (n = 68); and high (n = 46) clinical suspicion of TB. RESULTS: Based on comprehensive clinical diagnosis, sensitivity of the E-MTD test was 83%, 75%, and 87% for low, intermediate, and high clinical suspicion of TB, respectively, and corresponding specificity was 97%, 100%, and 100% (P = .25). Positive predictive value of the E-MTD test was 59% (low), 100% (intermediate), and 100% (high) compared with 36% (low), 30% (intermediate), and 94% (high) for AFB smear. Corresponding negative predictive values were 99%, 91%, and 55% [corrected] (E-MTD test) vs 96%, 71%, and 37% (AFB smear). CONCLUSIONS: For complex diagnostic problems like TB, clinical risk assessments can provide important information regarding predictive values more likely to be experienced in clinical practice. For this series, a clinical suspicion of TB was helpful in targeting areas of the clinical spectrum in which nucleic acid amplification tests can make an important contribution.

Genotypic and phenotypic characterization of "Streptococcus milleri" group isolates from a Veterans Administration hospital population.

Because identification of the species within the "Streptococcus milleri" group is difficult for the clinical laboratory as the species share overlapping phenotypic characteristics, we wished to confirm biochemical identification with identification by 16S rRNA gene sequence analysis. Ninety-four clinical isolates previously identified as the "Streptococcus milleri" group were reclassified as S. anginosus, S. constellatus, or S. intermedius with the API 20 Strep system (bioMerieux Vikek, Hazelton, Mo.) and the Fluo-card (Key Scientific, Round Rock, Tex.). In addition, we determined the Lancefield group, hemolysis, colony size, colony texture, repetitive extragenic palindromic PCR (rep-PCR) pattern, and cellular fatty acid (CFA) profile (MIDI, Newark, Del.). 16S rRNA gene sequence analysis with 40 selected representative strains showed three distinct groups, with S. constellatus and S. intermedius found to be more closely related to each other than to S. anginosus, and further distinguished a biochemically distinct group of urogenital isolates within the S. anginosus group of isolates. Except for strains unreactive with the Fluo-card (8%), all S. anginosus and S. intermedius strains identified by sequencing were similarly identified by biochemical testing. However, 23% of the selected S. constellatus isolates identified by sequencing (9% of all S. constellatus isolates) would have been identified as S. anginosus or S. intermedius by biochemical tests. Although most S. anginosus strains formed one unique cluster by CFA analysis and most S. constellatus strains showed similar rep-PCR patterns, neither method was sufficiently dependable for identification. Whereas Lancefield group or lactose fermentation did not correspond to sequence or biochemical type, S. constellatus was most likely to be beta-hemolytic and S. intermedius was most likely to have a dry colony type. The most frequent isolate in our population was S. constellatus, followed by S. anginosus. There was an association of S. anginosus with a gastrointestinal or urogenital source, and there was an association of S. constellatus and S. intermedius with both the respiratory tract and upper-body abscesses.

Microscopic examination and broth culture of cerebrospinal fluid in diagnosis of meningitis.

We reviewed the results of microscopic Gram stain examination and routine culture for 2,635 cerebrospinal fluid (CSF) samples processed in an adult hospital microbiology laboratory during 55 months. There were 56 instances of bacterial or fungal meningitis (16 associated with central nervous system [CNS] shunt infection), four infections adjacent to the subarachnoid space, four cases of sepsis without meningitis, and an additional 220 CSF specimens with positive cultures in which the organism isolated was judged to be a contaminant. Because 121 of these contaminants were isolated in broth only, elimination of the broth culture would decrease unnecessary work. However, 25% of the meningitis associated with CNS shunts would have been missed by this practice. The most common cause of meningitis was Cryptococcus neoformans, followed by Streptococcus pneumoniae and Neisseria meningitidis. In 48 of 56 (88%) of cases, examination of the Gram-stained specimen revealed the causative organism. If patients who had received effective antimicrobial therapy prior to lumbar puncture are excluded, the CSF Gram stain is 92% sensitive. Microscopic examination incorrectly suggested the presence of organisms in only 3 of 2,635 (0.1%) CSF examinations. Thus, microscopic examination of Gram-stained, concentrated CSF is highly sensitive and specific in early diagnosis of bacterial or fungal meningitis.

Streptococcus bovis infection of the central nervous system: report of two cases and review.

Streptococcus bovis is an uncommon cause of meningitis and subdural empyema. We report one case each of meningitis and subdural empyema in which S. bovis biotype II was isolated from both the spinal fluid and blood. In one case, the organisms were seen on a gram-stained preparation of cerebrospinal fluid. The first patient presented with gastrointestinal symptoms of unknown etiology, was immunosuppressed, and recovered. The second patient presented with syncope, developed a subdural empyema, and died; at autopsy, a colonic adenoma was found. A review of the English-language literature revealed only 14 previously reported cases of meningitis due to S. bovis and no cases of subdural empyema due to S. bovis. These cases indicate the importance of complete laboratory identification of specific organisms and confirm the need for a thorough neurological examination and search for underlying gastrointestinal disease in cases of S. bovis infection.

Limited vs full microbiological investigation for the management of symptomatic polymicrobial urinary tract infection in adult spinal cord-injured patients.

Spinal cord-injured (SCI) patients often suffer from symptomatic polymicrobial urinary tract infection (UTI). The objective of this study was to evaluate the clinical outcome and cost-savings associated with antibiotic therapy based on limited vs full microbiological investigation of urine cultures in adult SCI patients with symptomatic polymicrobial UTI (> or = 2 organisms growing in urine cultures). In the first part of the study, a total of 40 evaluable patients were prospectively randomized in a single-blinded fashion to receive antibiotic therapy based on either limited (21 patients) or full microbiologic investigation (19 patients) of urine cultures. The practicality of a limited microbiological investigation was further examined in the second part of the study where 12 consecutive patients with symptomatic polymicrobial UTI initially had only limited microbiological investigation of urine cultures and received antibiotic therapy accordingly. When analyzing all patients in the study, the likelihood of adequate clinical response was not significantly different between those who received antibiotic therapy based on limited (28/33 = 85%) vs full (18/19 = 95%) microbiological investigation of urine cultures (P = 0.40). An average of 183 US dollars could be saved per patient by managing symptomatic polymicrobial UTI based on a limited vs a full microbiological investigation. These results suggest that in adult SCI patients with symptomatic polymicrobial UTI antibiotic therapy guided by a limited microbiological investigation may be practical, adequate and cost-saving.

Clinical microbiology of coryneform bacteria.

Coryneform bacteria are aerobically growing, asporogenous, non-partially-acid-fast, gram-positive rods of irregular morphology. Within the last few years, there has been a massive increase in the number of publications related to all aspects of their clinical microbiology. Clinical microbiologists are often confronted with making identifications within this heterogeneous group as well as with considerations of the clinical significance of such isolates. This review provides comprehensive information on the identification of coryneform bacteria and outlines recent changes in taxonomy. The following genera are covered: Corynebacterium, Turicella, Arthrobacter, Brevibacterium, Dermabacter. Propionibacterium, Rothia, Exiguobacterium, Oerskovia, Cellulomonas, Sanguibacter, Microbacterium, Aureobacterium, "Corynebacterium aquaticum," Arcanobacterium, and Actinomyces. Case reports claiming disease associations of coryneform bacteria are critically reviewed. Minimal microbiological requirements for publications on disease associations of coryneform bacteria are proposed.

Helicobacter pylori does not migrate from the antrum to the corpus in response to omeprazole.

BACKGROUND: Omeprazole is known to have an effect on Helicobacter pylori in vivo. One opinion is that H. pylori "migrates" from the antrum to the corpus in response to omeprazole therapy. METHODS: To determine whether H. pylori migrates in response to omeprazole, we assessed the presence of H. pylori in the antrum and corpus in duodenal ulcer patients receiving omeprazole for 4 wk. Culture and histological examination of antral biopsies (Genta stain) were performed before patients received omeprazole, at the end of therapy, and 4-6 wk later. The end points were presence or absence of H. pylori and the number of H. pylori colonies per biopsy. RESULTS: Seventy-two patients had H. pylori in both the antrum and corpus at entry and 4-6 wk after ending therapy. Three general patterns were prevalent at the end of omeprazole therapy: antrum- and corpus-positive (54%), antrum-negative and corpus-positive (24%), both antrum- and corpus-negative (21%), and one patient had antrum-positive with corpus-negative (1%). Evaluation of the number of colonies per biopsy in those who remained H. pylori-positive in both the antrum and corpus throughout showed that the number of H. pylori decreased in both the antrum and corpus during therapy (507 +/- 60 vs. 225 +/- 51, p < 0.01 and 415 +/- 58 vs. 290 +/- 46 0.1) for antrum and corpus, respectively, and tended to return to pre-therapy levels 4-6 wk later. The number of H. pylori in the corpus also decreased in the antrum-negative and corpus-positive group during therapy with omeprazole (433 +/- 87 vs. 185 +/- 61, p < 0.05). In most of the patients studied, the number of H. pylori in the corpus was less posttreatment than it was pretreatment. The decrease in H. pylori load was also reflected in the development of false-negative urea breath tests. CONCLUSIONS: Omeprazole is detrimental to H. pylori in both the antrum and the corpus; migration from the antrum to the corpus in response to omeprazole is a myth.

Characterization of two unusual clinically significant Francisella strains.

We have isolated two phenotypically distinct nonfastidious Francisella strains (Fx1 and Fx2) from the blood of compromised patients with pneumonia and compared them with eight other Francisella strains, including Francisella tularensis biovar tularensis, F. tularensis biovar novicida, and F. philomiragia. Our isolates grew well on sheep blood agar, chocolate agar, modified Thayer-Martin agar, and Trypticase soy agar. Fx1 and Fx2 were determined to be within the Francisella genus by cellular fatty acid analysis and by the utilization of glucose, production of H2S and catalase, and lack of motility, oxidase, nitrate reductase, and gelatinase. They were additionally shown to belong to the species F. tularensis by sequencing of two variable regions comprising approximately 500 nucleotides of the 16S rRNA gene. Also, RNA probe hybridization confirmed their belonging to the species F. tularensis. However, the new strains, which are not identical, are distinguished from other F. tularensis strains by growth characteristics, repetitive extragenic palindromic PCR fragment pattern, and some biochemical tests. Key biochemical differences included the findings that Fx1 was positive for beta-galactosidase and arabinose hydrolysis and that both strains were citrulline ureidase positive and glycerol negative. Commercial F. tularensis antiserum agglutinated stock F. tularensis strains but not Fx1, Fx2, F. tularensis biovar novicida, or F. philomiragia; serum from either patient failed to agglutinate or only weakly agglutinated commercial antigen but showed agglutination when tested against each patient's respective isolate. Fx1 and Fx2 produced beta-lactamase. Because of their good growth, negative serology, and biochemical profile, the organisms could be misidentified in the clinical laboratory if standard strategies or commercial identification systems are used.

Uncertain clinical significance of duodenal mucosal abnormalities in HIV-infected individuals. Results of a case-control study.

Previous research has described abnormalities of duodenal mucosal morphology in human immunodeficiency virus (HIV)-infected individuals. We wanted to determine the frequency of disturbed villus architecture and investigate its relationship to HIV-related chronic diarrhea. We conducted a case-control study of 120 HIV-infected men, 63 with and 57 without chronic diarrhea. Stools were cultured for bacteria and examined for ova and parasites; esophagogastroduodenoscopy and flexible sigmoidoscopy with mucosal biopsies were performed. Biopsy tissue was examined using light and electron microscopy to detect enteric pathogens and to evaluate mucosal morphology. The mean CD4+ cell count was 143/min3, and enteric pathogens were detected in 56 of 120 men (47%). In approximately half the study sample (57%), duodenal villus architecture was normal; complete villus flattening was not observed. We detected no association between chronic diarrhea and altered villus architecture. Although further study is needed to clarify the pathogenesis of altered duodenal mucosal morphology, our results suggest that the clinical significance of the abnormalities may be small.

Quantitative light microscopic detection of Enterocytozoon bieneusi in stool specimens: a longitudinal study of human immunodeficiency virus-infected microsporidiosis patients.

The clinical course of microsporidiosis caused by Enterocytozoon bieneusi and the pattern of intestinal shedding of spores have not been correlated, at least in part because detection of E. bieneusi in stools is more difficult than detection of other protozoa because of its smaller size and less intense staining. We examined with a modified trichrome stain 124 stool specimens collected over a 2-year follow-up period from 23 human immunodeficiency virus-infected patients with electron microscopic-proven E. bieneusi infection and correlated the results with electron microscopic observations from duodenal biopsy specimens taken at the beginning of the study period. E. bieneusi was detected in the stool at least once in 74% (17 of 23) of all patients, in 100% (9 of 9) of patients in whose tissue moderate or abundant numbers of parasites were seen, and in 57% (8 of 14) of patients in whose tissue few parasites were seen. In two patients with abundant tissue parasites, many microsporidia were detected in every stool specimen (13 of 13) during the follow-up period, whereas among the patients with few tissue parasites, only 23% (15 of 64) of stool specimens were positive. Furthermore, if spore stages as well as plasmodial stages were detected in tissue, stool specimens were more likely to be positive. Although most of the heavily infected stools were from patients with chronic diarrhea, microsporidia were detected in 33, 28, and 42% of stool specimens from patients with nil, intermittent, and chronic diarrhea patterns, respectively. Although quantitation of E. bieneusi spores in stool specimens was closely correlated with quantitation in tissue, it was not correlated with reported patterns of diarrhea.