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SettingUrban health clinic, Nairobi.ObjectiveTo evaluate the impact on tuberculosis (TB) case detection and laboratory workload of reducing the number of sputum smears examined and thresholds for diagnosing positive smears and positive cases.DesignIn this prospective study, three Ziehl-Neelsen stained sputum smears from consecutive pulmonary TB suspects were examined blind. The standard approach (A), > or = 2 positive smears out of 3, using a cut-off of 10 acid-fast bacilli (AFB)/100 high-power fields (HPF), was compared with approaches B, > or = 2 positive smears (> or = 4 AFB/100 HPF) out of 3, one of which is > or = 10 AFB/100 HPF; C, > or = 2 positive smears (> or = 4 AFB/100 HPF) out of 3; D, > or = 1 positive smear (> or = 10 AFB/100 HPF) out of 2; and E, > or = 1 positive smear (> or = 4 AFB/100 HPF) out of 2. The microscopy gold standard was detection of at least one positive smear (> or = 4 AFB/100 HPF) out of 3.ResultsAmong 644 TB suspects, the alternative approaches detected from 114 (17.7%) (approach B) to 123 cases (19.1%) (approach E) compared to 105 cases (16.3%) for approach A (P < 0.005). Sensitivity ranged between 82.0% (105/128) for A and 96.1% (123/128) for E. The single positive smear approaches reduced the number of smears by 36% compared to approach A.ConclusionReducing the number of specimens and the positivity threshold to define a positive case increased the sensitivity of microscopy and reduced laboratory workload.

Type

Journal article

Journal

The international journal of tuberculosis and lung disease : the official journal of the International Union against Tuberculosis and Lung Disease

Publication Date

09/2007

Volume

11

Pages

953 - 958

Addresses

Epicentre, Paris, France. maryline.bonnet@geneva.msf.org

Keywords

Sputum, Humans, Mycobacterium tuberculosis, Tuberculosis, Pulmonary, Specimen Handling, Bacteriological Techniques, Reproducibility of Results, Predictive Value of Tests, Adult, Urban Population, Workload, Kenya, Female, Male