Enzyme-linked immunosorbent assay (ELISA) with mycobacterial crude antigens for the sero-epidemiological diagnosis of active tuberculosis.

In search for reliable, nonexpensive procedures for tuberculosis diagnosis suitable for seroepidemiological studies in leprosy-endemic areas, enzyme-linked immunosorbent assays (ELISAs) with whole intact bacilli, whole lipid-free bacilli and protein-enriched soluble extracts from the H37Rv Mycobacterium tuberculosis strain were evaluated. Sera tested came from 47 active, pulmonary tuberculosis adult cases, 60 household contacts of active tuberculosis cases, 20 lepromatous leprosy adult patients, and 67 healthy adult controls obtained from low and high leprosy and tuberculosis endemicity areas. There was no influence of such endemicity levels in the number of positive results in control sera. Antibody levels obtained with each of the antigens in ELISAs were significantly different in tuberculosis patients and the control groups. Ten percent of tuberculosis contacts were positive with some of the antigens and three of them showed suggestive chest radiographs. The best combination for a high number of positive results with tuberculosis sera and low positive results with leprosy sera was the BCG soluble extract (91% and 15%, respectively). This preparation also yielded excellent sensitivity and specificity values for tuberculosis (91.5% and 92.5%, respectively). These data suggest that BCG soluble extract ELISAs could provide helpful information to estimate tuberculosis prevalence only in leprosy-free areas, under a situation of unavailability of purified antigens. In pulmonary cases, sputum microscopic examination and culture have higher sensibility than serodiagnosis; therefore, the utilization of BCG soluble extract ELISAs as a diagnostic aid in individual patients with suspected active tuberculosis only can be useful in extrapulmonary cases.

Comparative assessment of the leprosy antibody absorption test, Mycobacterium leprae extract enzyme-linked immunosorbent assay, and gelatin particle agglutination test for serodiagnosis of lepromatous leprosy.

A comparative assessment of three serological methods for leprosy diagnosis (the fluorescent leprosy antibody absorption [FLA-ABS] test, the Mycobacterium leprae soluble-extract enzyme-linked immunosorbent assay [ELISA], and the M. leprae particle agglutination [MLPA] test) was carried out. The objective was to identify their performance in clinical and epidemiological diagnosis of leprosy. The study group included 45 lepromatous leprosy patients under treatment. Specificity was > 95% for all three assays, and sensitivity was 95, 58, and 74% for the FLA-ABS test, the MLPA test, and the ELISA, respectively. The only cross-reactivity for M. tuberculosis-infected patients was with the soluble-extract ELISA. Although the FLA-ABS test displayed the highest specificity and sensitivity values, it can only be used in well-developed laboratories, and the patient's clinical and epidemiological background must be considered when results are interpreted because the test remains positive after therapeutic success and could be positive for some household contacts. The MLPA test is easier to perform and interpret, and it is adequate for small laboratories and epidemiological studies intended to detect active untreated or irregularly treated leprosy cases. Therefore, the FLA-ABS and MLPA tests are complementary, and both should be used for serodiagnosis of leprosy.

Prospective immunological follow-up in household contacts of Mexican leprosy patients.

A 6-year prospective study of 79 household contacts of leprosy cases was made in order to correlate the development of the disease with their specific T-cell immunity, measured by the Mitsuda test, and levels of anti-Mycobacterium leprae antibodies determined in three consecutive observations with the FLA-ABS test. Overall in the contacts, 71.7% were Mitsuda positive and 93.6% showed seropositivity, without regard to their age, sex, or leprosy type of their index case. Households were divided into lower-risk and higher-risk groups according to either the paucibacillary or multibacillary character of their index case. The lower-risk group consisted of 19 contacts of 2 tuberculoid (TT) and 5 indeterminate cases. The higher-risk group was made up of 60 household contacts of 18 active lepromatous (LL) cases. All but two contacts in the former group had a positive Mitsuda reaction; the most common antibody titer was 1:160, with a tendency to stabilize or decrease over time. In the two Mitsuda-negative contacts, increased antibody levels were observed. In the higher-risk group, 61.6% were Mitsuda positive and showed a humoral profile similar to those Mitsuda positive in the lower-risk group. In most of the Mitsuda-negative LL contacts, the antibody levels remained constant or progressively increased, suggesting a high probability of active subclinical infection. This assumption was partially supported by the finding of a new borderline lepromatous (BL) leprosy case in the Mitsuda-negative LL contact group. Nevertheless, the contribution of the close and extensive contact with a multibacilliferous case as a risk factor was difficult to evaluate because of the small size of the sample studied.

Sensitivity and specificity of the FLA-ABS test for leprosy in Mexican populations.

The epidemiological surveillance for leprosy must include several clinical and laboratory procedures. The FLA-ABS test of Abe could be a useful tool for this purpose because it allows the demonstration of an effective contact with Mycobacterium leprae. In order to establish the specificity, sensitivity, and predictability of the FLA-ABS test under Mexican conditions, we studied sera collected from six groups of individuals: 60 healthy donors from a nonendemic area, 57 cases hospitalized for conditions other than infectious diseases from a general hospital in a nonendemic area, 72 patients with active pulmonary tuberculosis, 26 healthy individuals from an endemic area, 100 patients with polar lepromatous leprosy (LLp), and 123 household contacts of patients with LLp. The FLA-ABS test was negative with sera from the first four groups. Strong positive reactions were found in all LLp patients except one; the false-negative results could be attributed to successful treatment and a long-standing cure in this patient. Analysis of these results shows 100% specificity, 99% sensitivity, and predictability values of the test of 100% for positive results and 99% for negative ones. In addition, none of the 20 randomly selected sera from LLp patients were positive with crossreacting mycobacteria. Because 87.8% of the household contacts were positive in the absence of clinical manifestations of leprosy, it is possible to conclude that a positive result by itself is not enough to establish an early diagnosis of the disease, especially among inhabitants of endemic areas.(ABSTRACT TRUNCATED AT 250 WORDS)