Detection and diagnosis of Mycobacterium tuberculosis.

Tuberculosis continues to be a major health problem worldwide, affecting millions of people each year. Accurate and rapid diagnosis is key to controlling the disease, yet the traditional tests for TB produce results that are either inaccurate or take too long to be definitive. A fast and reliable diagnostic method that would differentiate between active and latent TB infection is also lacking. The current routine diagnostic tests for TB - chest x-ray, tissue culture, tuberculin skin test (TST) and acid-fast staining - all have their limitations. A chest x-ray alone is inconclusive; a tissue culture takes too long to produce a result; the TST lacks specificity and reliability; and acid-fast staining depends on a large number of bacteria in the sputum to give an accurate reading. Serological tests using different TB antigens to detect Mycobacterium tuberculosis infection are fast but lack the desired sensitivity. New methods have been developed, such as nucleic acid amplification technology which, although specific, can yield false-positive results. Immunologic tests (QuantiFERON and T-SPOT.TB), which measure the production of IFN-gamma by TB-specific T lymphocytes after encountering M. tuberculosis antigens, have certain advantages over the conventional tests, but they also have their disadvantages and unanswered questions. The need remains for a cost-effective, accurate and rapid method of diagnosing both active and latent TB infection.

Detection of genital colonization of group B streptococci during late pregnancy.

OBJECTIVE: To detect group B streptococcal carrier state of Saudi females during 3rd trimester of pregnancy and to assess type of specimens and the techniques used for the organism detection. METHODS: A total of 867 consecutive vaginal and rectal swabs were obtained from 217 pregnant women at > 28 weeks of gestation and their follow up testing from King Khalid University Hospital, Riyadh, Kingdom of Saudi Arabia. Swab-specimens were cultured comparatively on Islam and Edwards blood agar plates, and into selective Lim broth. Enrichment Lim broth cultures (>12 hours) with and without positive modified coagglutination test were then subcultured on Islam and Edwards sheep blood agar plates. Presumptive colonies were then tested for group B streptococcus identity by convential biochemical reactions, serogrouping and serotyping. Collected neonatal swab-specimens (184) were also treated similarly. RESULTS: In comparison to Lim broth enrichment culture, the direct swab specimen culture on Edwards blood agar or Islam agar plates technique revealed 84% sensitivity and 100% specificity, whereas modified coagglutination test after selective Lim broth enrichment revealed 100% sensitivity and 96% specificity. Group B streptococcus was isolated in at least one of the specimens from the 217 patients in 66 cases. Of these 66 cases, group B streptococcus was isolated from both vaginal and rectal swabs in 33 (50%) cases and only from vaginal swabs in 22 (33%) and rectal swabs in 11 (17%) cases. Of the group B streptococcus positive cases, 10 (15%) cases had spontaneously lost their carriage, upon follow up testing, whereas out of the 151 negative cases, 4 (2.6%) cases became positive for group B streptococcus colonization upon follow up testing with an overall carriage rate of (60/217) 27.6%. Certain demographic factors were found to alter such rate of carriage. Additionally, 50% of group B streptococcal colonized mothers vertically transmitted the homologous serotypes of the organism to their newborns, but clinical infection was not recorded during the study period. CONCLUSION: Group B streptococci colonization rate among term Saudi pregnant women is relatively high (27.6%); and thereby constitutes a group of women whose infants are at great risk of early-onset invasive disease. The modified coagglutination test after growth amplification seems rapid and cost-effective to detect lightly or heavily group B streptococcal colonized women. Vaginal and rectal swab specimens at late pregnancy appeared necessary to accurately identify group B streptococcus maternal colonization.