Comparison of different methods and times for reading the tuberculin skin test.

BACKGROUND: Current guidelines vary on the recommended method and time for measuring tuberculin skin test (TST) indurations. OBJECTIVE: To evaluate the best time and method for assessing TST results and which purified protein derivative (PPD) to administer. DESIGN: Standard PPD (PPD-S) and PPD-RT23 were applied concurrently on each forearm in random order in 78 nurses. MEASUREMENTS: TST induration was measured at 48, 72 and 96 h by two nurses by palpation and a ruler, palpation and a Vernier caliper, ballpoint pen and a ruler or ballpoint pen and a Vernier caliper. TST differences were assessed using mixed-effects analysis. We also assessed the rate of false-positive/-negative results and the variability of the TST measurements. RESULTS: We performed 767 TST measurements. The adjusted mean TST size was larger with PPD-S than with PPD-RT23 (12.8 vs. 10.8 mm, P < 0.001), and at 72 h than at 48 h and 96 h (13.4 vs. 11.8 vs. 10.1 mm, P < 0.05). The smallest number of false results was observed with PPD-S, the ballpoint pen-ruler and at 72 h; palpation+ruler had the least variability at 72 h. CONCLUSIONS: The TST should ideally be performed with PPD-S and measured at 72 h with the ballpoint pen+ruler or palpation+ruler methods.

Risk factors for developing tuberculosis: a 12-year follow-up of contacts of tuberculosis cases.

BACKGROUND: Many risk factors for the development of tuberculosis (TB) have been reported but have not been simultaneously assessed. OBJECTIVE: To determine the risk of developing TB associated with each risk factor, after adjusting for all others. METHODS: We performed a population-based, retrospective cohort study of the contacts of TB cases recorded in British Columbia, Canada. Known risk factors for the development of TB were assessed over a 12-year period; Cox regression was used to estimate the hazard ratios (HRs) of TB, adjusting for the other factors. RESULTS: Among 33 146 TB contacts, 228 developed TB during the study period (TB rate 668 per 100,000 population, 95%CI 604-783). The main risk factors for TB development were malnutrition (HR 37.5), no treatment of latent TB infection (HR 25) or <6 months of treatment (HR 5.38), age 0-10 years (HR 7.87), being a household contact (HR 8.47) and having a tuberculin skin test induration of >or=5 mm (HR >or=4.99). Bacille Calmette-Guérin vaccination significantly reduced the risk of TB development (HR 0.32, 95%CI 0.20-0.50). CONCLUSIONS: Among contacts of TB cases, we have identified the few factors that carry a very high risk for developing TB. These factors identify populations at highest risk and permit more effective TB control.

Cost-effectiveness of a new interferon-based blood assay, QuantiFERON-TB Gold, in screening tuberculosis contacts.

BACKGROUND: Recent approval of interferon-gamma release assays that are more specific for Mycobacterium tuberculosis has given new options for the diagnosis of latent tuberculosis infection (LTBI). OBJECTIVE: To assess the cost-effectiveness of Quanti-FERON-TB Gold (QFT-G) vs. the tuberculin skin test (TST) in diagnosing LTBI in contacts of active TB cases using a decision analytic Markov model. METHODS: Three screening strategies--TST alone, QFT-G alone and sequential screening of TST then QFT-G--were evaluated. The model was further stratified according to ethnicity and bacille Calmette-Guérin (BCG) vaccination status. Data sources included published studies and empirical data. Results were reported in terms of the incremental net monetary benefit (INMB) of each strategy compared with the baseline strategy of TST-based screening in all contacts. RESULTS: The most economically attractive strategy was to administer QFT-G in BCG-vaccinated contacts, and to reserve TST for all others (INMB CA$3.70/contact). The least cost-effective strategy was QFT-G for all contacts, which resulted in an INMB of CA$-11.50 per contact. Assuming a higher prevalence of recent infection, faster conversion of QFT-G, a higher rate of TB reactivation, reduction in utility or greater adherence to preventive treatment resulted in QFT-G becoming cost-effective in more subgroups. CONCLUSIONS: Selected use of QFT-G appears to be cost-effective if used in a targeted fashion.

Wood smoke-associated lung disease: a clinical, functional, radiological and pathological description.

BACKGROUND: Approximately half of the world's population, and up to 90% of households in rural areas of developing countries, depend on biomass for cooking and heating. SETTING: The National Institute of Respiratory Diseases, México City. OBJECTIVE: To describe wood smoke-associated lung disease (WSLD). DESIGN: Description of the clinical, functional and radiological manifestations of patients with WSLD, and a comparison of pathological findings of patients who died of WSLD and smokers who died of chronic bronchitis. RESULTS: All patients with WSLD were non-smoking women with chronic bronchitis, in whom asthma, bronchiectasis, tuberculosis, congestive heart failure, extreme obesity and alfa-1 antitrypsin deficiency had been excluded. All patients used wood for cooking and had been exposed to wood smoke for a median of 45 years. Dyspnoea, airway obstruction, air trapping, increased airway resistance, pathological evidence of anthracosis, chronic bronchitis, centrilobular emphysema and pulmonary hypertension were present in most patients with WSLD. Bronchial squamous metaplasia was a common finding. There were no significant differences in the histopathological findings between patients with WSLD and smokers. Diffuse interstitial fibrosis was absent in all patients. CONCLUSIONS: Patients with WSLD have obstructive lung disease, chronic bronchitis, emphysema and pulmonary hypertension comparable to smokers.

Tuberculin skin test size and risk of tuberculosis development: a large population-based study in contacts.

SETTING: Contacts of tuberculosis (TB) cases identified from eight Provincial databases in British Columbia, Canada, between 1990 and 2000. OBJECTIVE: To assess the risk of developing TB based on tuberculin skin test (TST) sizes in contacts of TB cases who did not receive treatment for latent TB infection. DESIGN: Retrospective, population-based cohort study with a 12-year follow-up. RESULTS: Among 26,542 contacts, 180 individuals developed TB (TB rate 678/100,000). Household contacts with a TST size 0-4 mm had a TB rate of 1014/100,000, those with 5-9 mm a TB rate of 2162/100,000 and those with 10-14 mm a rate of 4478/100,000. Children aged 0-10 years with 0-4 mm had a TB rate of 806/100,000, those with 5-9 mm a TB rate of 5556/100,000 and those with 10-14 mm a rate of 42,424/100,000. Immunosuppressed contacts with TST sizes 0-4 mm had a TB rate of 630/100,000, those with 5-9 mm a TB rate of 1923/100,000, and those with 10-14 mm a rate of 1770/100,000. CONCLUSIONS: TB rates were high for all TST sizes in household contacts, 0-10 year old contacts and immunosuppressed contacts. These contacts may benefit from treatment for latent TB infection, regardless of the size of their TST.