The relative frequency of Mycobacterium tuberculosis and Mycobacterium avium infections in HIV positive patients, Ahvaz, Iran

ObjectiveTo estimate the prevalence of Mycobacterium tuberculosis (M. tuberculosis) and Mycobacterium avium (M. avium) infections in HIV-positive patients suspected to have pulmonary and extrapulmonary mycobacterial co-infection using PCR technique.MethodsTotally 50 samples comprising sputum, pleural fluid and CSF taken from HIV positive patients suspected to have mycobacterial infection, were processed. The demographic information and results of acid fast staining and culture were recorded for each patient. The PCR for detecting of M. tuberculosis comprised of specific primers targeting IS6110 gene sequence. For detecting of M. avium, PCR with primers that amplifies the mig gene were used.ResultsFrom 50 samples processed, 45 were sputum (90%), 3 pleural fluid (6%) and 2 CSF (4%). In total, 8 (16%) were culture positive, 7 had positive acid fast staining (14 %) and 13 samples (26%) were positive using PCR technique. All the positive samples were sputum and belonged to patients with pulmonary infection. Of these, 9 were positive for M. tuberculosis (69.2%) and 4 were identified as M. avium (30.8%), which 2 out of 13 positive samples showed mixed infections by both mycobacteria.ConclusionsThe PCR shows the highest detection rate (26%) of mycobacteria compared with culture and acid fast staining. The majority of infections were with M. tuberculosis (18%) and this shows the importance of this mycobacterial co-infection in HIV positive patients in the region of study.     

Genetic and serovar typing of clinical isolates of the Mycobacterium avium-intracellulare complex

Setting: One hundred and thirty-four Mycobacterium avium-intracellulare complex (MAC) isolates were obtained from 121 patients in the UK.Objective: To compare serotyping and genetic analysis for species identification of MAC isolates from patients with and without the acquired immunodeficiency syndrome (AIDS).Design: Clinical MAC isolates were cultured and analyzed by serotyping, the commercially available Accuprobe kit, hybridization with genes coding for the 19 kDa and 38 kDa antigens of M. tuberculosis and fingerprinting with the pMB22 probe derived from M. paratuberculosis.Results: Species classification on the basis of genetic analysis was similar to serovar typing, with only exceptional discrepancies. Serovar prevalence was different in the two groups of patients, and different from those reported in other countries. MAC isolates from AIDS patients were exclusively M. avium, whereas patients without AIDS had MAC infections with M. avium and M. intracellulare in about equal proportion. M. intracellulare clinical isolates were genetically more heterogeneous than M. avium. Only M. intracellulare hybridized with the 38 kDa gene probe.Conclusions: Serovars are strongly linked with species in clinical MAC isolates, confirming results previously obtained with reference strains. M. intracellulare can be easily identified by the presence of a 38 kDa gene.     

Clinical features and treatment outcomes of Mycobacterium chimaera lung disease and antimicrobial susceptibility of the mycobacterial isolates

BackgroundMycobacterium chimaera, one of the Mycobacterium avium complex (MAC) members, was recently identified using modern gene sequencing analysis. Unlike M. avium and M. intracellulare, little is known about the clinical features, antimicrobial susceptibilities, and treatment outcomes of M. chimaera lung disease.MethodsThis study was conducted in a medical center from December 2012 to July 2015. Patients who fulfilled the 2007 ATS/IDSA diagnostic criteria for nontuberculous mycobacterial lung disease were enrolled. M. chimaera isolates were identified based on the findings of sequencing of rpoB gene, the internal transcribed spacer (ITS) region of the 16S–23S rRNA gene, and the heat-shock protein 65 gene (hsp65). Minimum inhibitory concentrations (MICs) of 13 antimicrobial agents were determined.ResultsDuring the study period, 247 patients with MAC lung disease were identified, and 11.3% (28/247) of the patients had lung disease caused by M. chimaera. Among these patients, 17 (60.7%) were female, and their median age was 72.5 (40–100) years. All M. chimaera isolates were susceptible to clarithromycin and rifabutin. All the isolates were resistant to moxifloxacin and only 10 (35.7%) and 2 (7.1%) were susceptible to amikacin and linezolid, respectively. Of the nine patients who received macrolide-based regimens, more achieved radiographic resolution than those treated with non-macrolide-based regimens (66.7% vs. 15.8%, P = 0.013), and they tended to have better survival (P = 0.10).ConclusionsA substantial portion (11.3%) of MAC lung disease cases were caused by M. chimaera, and treatment with macrolide-based regimens resulted in better clinical outcomes for patients with M. chimaera lung disease.     

Clinical significance and epidemiologic analyses of Mycobacterium avium and Mycobacterium intracellulare lung disease from post-marketing surveillance

Background

In Japan, nontuberculous mycobacterial lung disease is mostly attributable to Mycobacterium avium complex (MAC), i.e., M. avium or M. intracellulare. However, clinical features of the disease caused by these two pathogens have not been studied sufficiently yet.

Identification of Mycobacterium avium complex strains belonging to serovars 21–28 by three commercial DNA probe tests

Various reference strains of Mycobacterium avium complex (MAC) belonging to serovars 21–28 were identified by three DNA probe tests, i. e., Gen-Probe ^®, AccuProbe^™ and SNAP^® tests. All of these DNA probe tests were in agreement for strains identified as M. aviumor M. intracellulare. The tested serovar strains involved M. avium, M. intracellulare, MAC reactive only with Probe X of SNAP test (‘Probe X-reactive MAC’), M. scrofulaceum reactive with Probe X of SNAP test (‘Probe X-reactive M. scrofulaceum’), and typical M. scrofulaceum which did not react with any of the probes. Both reference strains belonging to serovar 21 were M. avium, and none of the other serovars included this species. On the contrary, M. intracellulare was found in serovars 22, 25, 26, and 28. ‘Probe X-reactive MAC’ were also widely found in serovars 23, 24, 26, 27, and 28, while ‘Probe X-reactive M. scrofulaceum’ was seen only in serovar 22. These results confirm the usefulness of SNAP test to identify the MAC showing no reactivity to Gen-Probe and AccuProbe.     

Pneumococcal Pneumonia Co-infection with Mycobacterium avium and Nocardia cyriacigeorgica in an Immunocompetent Patient

A 61-year-old woman was transferred with a complaint of a fever and productive cough. She had tested positive for Mycobacterium avium and Nocardia cyriacigeorgica at least twice, and Streptococcus pneumonia (PISP) was isolated (3+) from her purulent sputum. As radiological findings, a lower lung field-dominant infiltration shadow and nodular shadow with cavity were recognized in the bilateral lung fields. We diagnosed her with pneumococcal pneumonia co-infection with M. avium and N. cyriacigeorgica. She was treated with MEPM for pneumococcal pneumonia, a standard regimen containing clarithromycin for pulmonary M. avium complex (MAC) disease, and sulfamethoxazole/trimethoprim for pulmonary nocardiosis. She improved with appropriate treatment.     

Comparative assays of the rpoB gene for identification of Mycobacterium tuberculosis isolated from patients in Sudan.

OBJECTIVES: To characterise mycobacterial clinical isolates based on amplification of the rpoB gene. SETTING: One hundred and thirty-five mycobacterial isolates cultured from suspected pulmonary tuberculosis (TB) patients were identified phenotypically. Molecular characterisation of the isolates was performed based on amplification of the rpoB gene, using duplex polymerase chain reaction (DPCR), PCR-restriction fragment length polymorphism (RFLP) and nested PCR-based sequence analysis techniques. RESULTS: The DPCR assay identified 129 of 135 (95.5%) clinical isolates as Mycobacterium tuberculosis complex species. Restriction enzyme analysis of the rpoB PCR product using Hind II identified 134 of the 135 (99.3%) isolates as M. tuberculosis complex, while nested PCR sequence analysis of the rpoB gene identified 133/133 examined isolates (100%) as M. tuberculosis species. No mycobacteria other than M. tuberculosis (MOTT) were detected among the studied isolates. CONCLUSION: DPCR, PCR/RFLP Hind II and nested PCR sequence analysis of the rpoB gene techniques showed comparable efficiency in the characterisation of Mycobacterium isolates. Nested PCR sequence analysis of the rpoB gene was superior to PCR/RFLP for characterisation of suspected M. tuberculosis isolates, while the DPCR technique showed less sensitivity. As PCR-RFLP requires less sophisticated laboratory facilities than nested PCR sequence analysis, it would be more appropriate to be adopted for accurate characterisation of mycobacteria in countries with a weak infrastructure.     

Clinical Aspects of Pulmonary Nontuberculous Mycobacteriosis

Nontuberculous mycobacterial (NTM) infections are an emerging problem. Common organisms include Mycobacterium avium, M. intracellulare, and M. kansasii, along with the M. avium intracellulare complex (MAC), which includes both M. avium and M. intracellulare. Typically, NTM infections affect the lungs and subsequently demonstrate a chronic course. Therefore, persistent respiratory symptoms generally indicate of the presence of pulmonary NTM diseases, and chest radiography, along with a sputum examination, are essential for its diagnosis. Because NTM are ubiquitous environmental organisms, a positive culture from a minimum of two separate expectorated sputum samples are required to make a diagnosis. The repertoire of effective drugs for treatment is considerably limited, indicating the need for long-term management with multiple drugs. Establishing a treatment regimen with high therapeutic efficacy and safety is an important issue for the future.     

Isolation and characteristics of Mycobacterium avium complex from water and soil samples in Uganda

Setting: Mycobacterium avium complex organisms have not been isolated from late stage AIDS patients in Uganda. This could possibly be due to the absence of M. avium complex in the Uganda environment.Objective and Design: Determine whether M. avium complex organisms could be isolated from water and soils collected in the living environment of Ugandan AIDS patients.Results: Representatives of the M. avium complex were isolated from 3 of 7 (43%) water and 3 of 7 (43%) soil samples collected in Kampala, Uganda. The average number of colony-forming units per ml water was 3.3 and average colony-forming units per gram of soil was 7825. In terms of growth characteristics, antimicrobial susceptibility patterns, and the presence or absence of plasmids and IS901, Ugandan M. avium complex isolates were similar to those isolated from the US and European AIDS patients and their environment.Conclusion: M. avium complex organisms sharing genetic and physiological characteristics of M. avium complex isolates recovered from patients with AIDS can be isolated from water and soil samples in Uganda.     

Risk factors for hemoptysis in Mycobacterium avium complex lung disease

BackgroundHemoptysis is a frequent and sometimes fatal complication of non-tuberculous mycobacterial (NTM) lung disease. The risk factors for hemoptysis are not well understood. In the current study, potential risk factors for hemoptysis were investigated in patients with Mycobacterium avium complex (MAC) lung disease, which is the most common NTM in Japan.MethodsMedical records from the Kinki-Chuo Chest Medical Center were reviewed. Consecutive patients with MAC lung disease diagnosed in 2014 and followed up for more than 1 year in the hospital were included in the study. Hemoptysis was confirmed between 2014 and 2016. The characteristics of patients with hemoptysis and non-hemoptysis at the time of the initial diagnosis of MAC lung disease were obtained from the medical records, and the two groups were compared. The radiological findings assessed included nodules, infiltration shadows, cavities, and bronchiectasis. Each was classified and scored individually in six lung fields, and these data were used to generate radiological scores.ResultsThe study included 82 patients with MAC lung disease, 18 with hemoptysis and 64 without. Higher total radiological severity score at the time of the initial diagnosis of MAC was associated with an increased risk of hemoptysis. Among the radiological scores, infiltration and cavities were marginally associated with the risk of hemoptysis.ConclusionsThe radiological severity score at the time of initial diagnosis of MAC lung disease was associated with hemoptysis.     

Clinical application of microplate DNA-DNA hybridization procedure for rapid diagnosis of mycobacterial infections

Setting: As an alternative to biochemical analysis, microplate DNA-DNA hybridization was applied for rapid diagnosis of mycobacterial infection.Objective: To assess how rapidly and correctly the microplate hybridization method can progress from clinical sample to final species identification of mycobacteria.Design: Clinical samples (pooled sputa or bronchial lavage fluid) were obtained from patients. Depending on the estimated bacterial amounts, genetic identification was performed either directly or following primary culture. Extracted DNA labeled by photobiotin was hybridized in microdilution wells with type-strain DNAs from 4 species (Mycobacterium tuberculosis, M. avium, M. intracellulare, and M. kansasii), then identified on the basis of genetic relatedness, which was quantitated by colorimetric detection.Results: With samples containing more than 10⁸ colony-forming units [CFU](5 cases), species identification was successfully performed on the day of sample preparation. With samples of not more than 10⁷ CFU (14 cases), although 4–21 days' primary culture were necessary, species were also correctly identified by the microplate method. Furthermore, M. avium and M. intracellulare were distinctly identified. All the results precisely corresponded to those of biochemical analysis, which took 4–12 weeks to complete identification.Conclusion: We consider that microplate DNA-DNA hybridization is a dependable technique for rapid diagnosis of mycobacterial infection.     

Pattern of utilization of rifabutin for prophylaxis of Mycobacterium avium complex among patients with advanced human immunodeficiency virus disease in a community setting

Objective: To characterize the pattern of utilization, effectiveness, and safety profile of rifabutin for Mycobacterium avium complex (MAC) prophylaxis among individuals with advanced human immunodeficiency virus disease in a community setting.Methods: Individuals who, while registered in the provincial drug distribution program, had at least one CD4 count below 100 cells/mm³ for the period 1 May 1993 to 31 March 1994 were included. MAC diagnoses were identified through a record linkage with the mycobacterial reference laboratory of the Provincial Centre for Disease Control. In order to determine the occurrence of adverse events, a survey was sent in March 1994 to the 98 primary care physicians prescribing rifabutin prophylaxis in the province. We achieved 100% response rate to the survey.Results: During the study period 515 patients in our drug treatment program were eligible to receive MAC prophylaxis. Of these, 340 (66%) were being prescribed rifabutin as recommended by current guidelines. Rifabutin prophylaxis use was significantly associated with use of antiretroviral therapy. The product limit estimate of the cumulative incidence of MAC at 10 months was 13.0% among those receiving rifabutin prophylaxis. Diagnosis of MAC was significantly associated with a lower baseline CD4 count (cumulative incidence 7.1 % and 18.1 % for CD4 ≥ 50 and < 50 cells/mm³, respectively, P = 0.01). A total of four cases of uveitis, eight cases of pseudo-jaundice, and five cases of arthralgia in 16 patients were identified by our survey.Conclusion: Our data demonstrates that rifabutin prophylaxis of MAC is being used by approximately 66% of eligible individuals. Rifabutin use was associated with antiretroviral use, which may reflect individuals' attitudes towards medications. Our intention-to-treat analysis, with a 10 month cumulative MAC incidence of 13.0% among those receiving rifabutin prophylaxis, is in keeping with break-through rates previously reported in the context of clinical trials. Our results also support previous observations that the risk of MAC infection greatly increases at CD4 counts < 50 cells/mm³. Rifabutin prophylaxis was generally well-tolerated in our program.     

Six years' experience with the discontinuation of BCG vaccination: 4. Protective effect of BCG vaccination against the Mycobacterium avium intracellulare complex

Setting: In 1986, mass BCG vaccination of newborns was discontinued in an extensive territorial sample of neonates in the Czech Republic (30 000 infants annually). The non-vaccinated children have since been tuberculin tested at two-year intervals; those with continual or repeated intensive contact with animals in households or on farms were also tested with Mycobacterium avium intracellulare complex sensitin in addition to tuberculin.Objective: Within the frame work of the surveillance programme the incidence of infection and disease caused by M. avium intracellulare complex M. avium complex) was evaluated and the protective effect of BCG vaccination analysed.Design: In 1986–1993, out of 190 874 non-vaccinated children, 36 were found to be infected by M. avium complex; 27 of them developed disease, i.e. mycobacteriosis other than tuberculosis (MOTT).Results: The annual risk of infection with M. avium complex was 4.8/100 000 children per year, of whom 3.6/ 100 000 developed mycobacteriosis. 24 patients suffered from swelling of cervical lymph nodes, 2 of mediastinal lymph nodes and one child had the disease localized both in cervical and mediastinal lymph nodes. The disease was verified bacteriologically in 9 children. Most of the diseased children had impaired immunity; a marked skin reactivity of M. avium complex sensitin was present in all infected children.Animal sources infected by M. avium complex were detected in 5 cases. Another 14 children also had close contact with animals but without proven M. avium complex infection.Conclusion: In non-BCG vaccinated children the incidence of lymphadenitis caused by M. avium complex was considerably higher than in vaccinated children. BCG cells possess antigenic determinants which confer protective immunity probably both against M. tuberculosis and against M. avium complex infections. It may thus be assumed that BCG vaccination protects both against pathogenic tubercle bacilli and M. avium complex. This should be taken into consideration before recommending discontinuation of mass BCG vaccination of newborns in areas with a high prevalence of M. avium complex infection.     

In vitro activities of 2,2′-bipyridyl analogues against Mycobacterium avium and M. tuberculosis

Setting: Because of widespread emergence of resistant Mycobacterium tuberculosis and the high incidence of opportunistic infection caused by M. avium complex (MAC) in AIDS patients, there is an urgent need for new drugs against these organisms.Objective: To evaluate the activity of newly synthesized 2′2-bipyridyl analogues against MAC and M. tuberculosis.Design: Susceptibility of MAC and M. tuberculosis to VUF-8514 and VUF-8842 were determined by both tube dilution method using 7H9 broth and radiometric (BACTEC) method using ¹⁴C-palmitic acid.Results and Conclusions: The MICs of 8514 against MAC and M. tuberculosis wee 1 μg/ml and 0.5 μg/ml respectively, while for 8842 the respective values were 8 μg/ml and 2 μg/ml. In general, the MBC values for both drugs were two-fold higher than their corresponding MIC values. However, both drugs exhibited high bactericidal activities against both organisms. The MICs of clinical isolates of both organisms were in the same range as reference strains; furthermore, two isolates of M. tuberculosis that showed resistance to rifampicin were found to be susceptible to 8514. Thus, these two bipyridyl analogues show great promise in chemotherapy of tuberculosis and M. avium infection.     

Identification of Mycobacterium avium, Mycobacterium intracellulare, and Mycobacterium tuberculosis complex by Gen-Probe Rapid Diagnostic System

DNA probe testing for Mycobacterium avium, Mycobacterium intracellulare and Mycobacterium tuberculosis complex (MTC) was performed using Gen-Probe Rapid Diagnostic System (Gen-Probe Inc., San Diego, Calif., U.S.A.). By DNA probe test carried out blindfold for 48 mycobacterial strains with code numbers obtained from Kyoto University (Prof. F. Kuze), 13, 7, and 5 strains were identified as to be M. avium, M. intracellulare, and MTC, respectively. The diagnostic specificity and sensitivity of this testing were 100%. In this experiment, % hybridization of M. avium complex (MAC) and MTC were 25-55% and 45-52%, respectively. DNA probe test for 54 MTC strains including M. tuberculosis, M. bovis, M. africanum and M. microti revealed that 53 strains, except for one strain donated as a niacin-negative M. tuberculosis, reacted with MTC probe but not with MAC-probes. The one exceptional strain reacted with both the MTC- and M. avium-probes. However, when ten colonies randomly isolated from this strain on 7H11 agar plate were subjected to the DNA probe test again, all of these colonies reacted with M. avium probe, but not with MTC probe. Moreover, one representative colony was found to have alpha-antigen specific for the MAC.     

Genetics study and transmission electron microscopy of pili in susceptible and resistant clinical isolates of Mycobacterium tuberculosis

ObjectiveTo study genetic bases and morphology of pili in Mycobacterium tuberculosis (M. tuberculosis).MethodsPCR and sequencing were used to investigate two related pili, Mtp and Flp genes in clinical isolates of M. tuberculosis. The primers were designed and PCR program were set for whole genes amplification. PCR products of the two genes from all isolates were sequenced by an applied biosystems apparatus and the results were analysed by online software. In the other hands, harvested cells from fresh cultures of isolates were undergoing specific sample preparation for sectional and negative staining for transmission electron microscopy.ResultsElectrophoresis revealed two specific bonds of 361 bp for Mtp and 150 bp for Flp genes and confirmed primer and PCR conditions designing. There were not any mutations in sequencing results of Mtp and Flp in comparison with reference sequence. Transmission electron microscopy examination revealed two distinct types of pili in the isolates as a bundle-forming pilus and rope-like pilus. From total investigated cells, 10% harbored pili in their structure.ConclusionsTwo genes of pili in all clinical isolates of M. tuberculosis were conserved and two morphological types of pili were detected. We proposed that by targeting pili proteins by a suitable inhibitor, it could affect the pathogenesis especially in resistant forms.     

Identification of Mycobacterium avium and Mycobacterium intracellulare using three DNA probe tests, and their distributions in Japan]

Identification of Mycobacterium avium complex (MAC) was made using three DNA probe tests for MAC: Gen-Probe Rapid Diagnostic System for the MAC (Gen-Probe Inc., San Diego, U.S.A.), AccuProbe MAC Culture Identification or Confirmation Test (Gen-Probe Inc.); and SNAP Culture Identification Diagnostic Kit (MAC) (Syngene Inc., San Diego, U.S.A.). Various strains of MAC belonging to serovars 21 to 28 were identified by the DNA probe tests and showed the following. First, Serovar 21 and 25 belonged to M. avium and M. intracellulare, respectively. Each of them reacted with species-specific probes used in the three DNA probe tests [i.e., either M. avium-probe (in SNAP test; Probe A) or M. intracellulare-probe (in SNAP test; Probe I)]. Second, serovars 22-24 and 26-28 consisted of M. intracellulare, MAC strains that reacted with Probe X of SNAP test but lacked the reactivity with M. avium- and M. intracellulare probes of all the DNA probe tests, M. scrofulaceum that showed no reactivity with M. avium- or M. intracellulare-probe or Probe X, and M. scrofulaceum that had only the reactivity with Probe X. When the disease-associated MAC strains (35 strains), isolated in the Kanto to Kyushu areas in Japan, were identified using AccuProbe test, both the M. avium and M. intracellulare strains identified by the Gen-Probe test reacted with the MAC-probe but not with the M. tuberculosis complex (MTC)-probe.(ABSTRACT TRUNCATED AT 250 WORDS)     

A novel repeat sequence specific to Mycobacterium tuberculosis complex and its implications

Restriction fragment length polymorphism analysis of Korean clinical isolates of Mycobacterium tuberculosis using a 245 bp fragment of IS6110 revealed a conserved 3.5 kb Pvull fragment. Attempts to clone this 3.5 kb fragment resulted in the serendipitous discovery of a novel repeat sequence present within a separate 3.5 kb Pvull genomic fragment. Nucleotide sequencing of a 823 bp region containing the putative repeat sequence revealed the presence of three small direct repeats, three palindromes and a 453 bp region that was analogous to 455 bp of a M. tuberculosis sequence previously reported.¹ The presence of this 453 bp repeat sequence was demonstrated in standard mycobacterial strains belonging to the M. tuberculosis complex, including the H37Rv, H37Ra, Erdman, and Canetti strains and M. bovis and M. bovis bacille Calmette-Guérin (BCG). Other mycobacterial species (M. kansasii, M. smegmatis, M. simiae, M. fortuitum, M. scrofulaceum, M. intracellulare, M. avium, and M. haemophilum) did not contain this sequence, suggesting that the 453 bp repeat sequence was specific to the M. tuberculosis complex. Of the 13 Korean and 12 other clinical isolates of M. tuberculosis tested, all contained three to four copies of the repeat sequence. The Southern blot patterns of the various M. tuberculosis strains allowed classification into five different groups. The most frequent pattern was the ‘BCG-type’ (4.7, 3.5, and 2.4 kb bands); the second most frequent pattern was the ‘4-band-type’ (13, 4.7, 3.5, and 2.4 kb), observed only in the Korean clinical isolates, and the third most common pattern was the M. tuberculosis H37Rv/H37Ra/M. bovis-type (13, 4.7, and 3.5 kb bands). Upstream sequences indicate proximity to the rhamnose biosynthesis (rfb) cluster of M. tuberculosis. Our results indicate that the repeat sequence may be useful for the design of probe and polymerase chain reaction primers for the identification and epidemiological testing of members of the M. tuberculosis complex.     

Sources of disseminated Mycobacterium avium infection in AIDS

OBJECTIVES: To identify the sources of disseminated Mycobacterium avium complex (MAC) infection in AIDS. METHODS: HIV positive subjects with CD4 counts <100/mm(3) in Atlanta, Boston, New Hampshire and Finland were entered in a prospective cohort study. Subjects were interviewed about potential MAC exposures, had phlebotomy performed for determination of antibody to mycobacterial lipoarabinomannin and for culture. Patient-directed water samples were collected from places of residence, work and recreation. Patients were followed for the development of disseminated MAC. Univariate and multivariate risk factors for MAC were analyzed. RESULTS: Disseminated MAC was identified in 31 (9%) subjects. Significant risks in univariate analysis included prior Pneumocystis carinii pneumonia (PCP) (hazard ratio 1.821), consumption of spring water (4.909), consumption of raw seafood (34.3), gastrointestinal endoscopy (2.894), and showering outside the home (0.388). PCP, showering and endoscopy remained significant in a Cox proportional hazards model. There was no association between M. avium colonization of home water and risk of MAC. In patients with CD4<25, median OD antibody levels to lipoarabinomannin at baseline were 0.054 among patients who did not develop MAC and 0.021 among patients who did develop MAC (P=0.077). CONCLUSIONS: MAC infection results from diverse and likely undetectable environmental and nosocomial exposures. Mycobacterial infection before HIV infection may confer protection against disseminated MAC in advanced AIDS.