Reducing the number of sputum samples examined and thresholds for positivity: an opportunity to optimise smear microscopy

Authors: Bonnet, M.1; Ramsay, A.2; Gagnidze, L.1; Githui, W.3; Guerin, P.J.1; Varaine, F.4

Source: The International Journal of Tuberculosis and Lung Disease, Volume 11, Number 9, September 2007 , pp. 953-958(6)

Publisher: International Union Against Tuberculosis and Lung Disease

Key:
Free Content - Free Content
New Content - New Content
Subscribed Content - Subscribed Content
Free Trial Content - Free Trial Content

Abstract:

SETTING: Urban health clinic, Nairobi.

OBJECTIVE: To 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.

DESIGN: In this prospective study, three Ziehl-Neelsen stained sputum smears from consecutive pulmonary TB suspects were examined blind. The standard approach (A), ≥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, ≥2 positive smears (≥4 AFB/100 HPF) out of 3, one of which is ≥10 AFB/100 HPF; C, ≥2 positive smears (≥4 AFB/100 HPF) out of 3; D, ≥1 positive smear (≥10 AFB/100 HPF) out of 2; and E, ≥1 positive smear (≥4 AFB/100 HPF) out of 2. The microscopy gold standard was detection of at least one positive smear (≥4 AFB/100 HPF) out of 3.

RESULTS: Among 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.

CONCLUSION: Reducing the number of specimens and the positivity threshold to define a positive case increased the sensitivity of microscopy and reduced laboratory workload.

Keywords: tuberculosis; microscopy; diagnosis

Document Type: Regular paper

Affiliations: 1: Epicentre, Paris, France 2: Liverpool School of Tropical Medicine, Liverpool, UK 3: Centre for Respiratory Diseases Research, Kenya Medical Research Institute, Nairobi Kenya 4: Médecins Sans Frontières, Paris, France

* This feature is in beta and some links may initially be displayed as numbers instead of article titles. Clicking on any of the links will take you to the recommended articles, regardless of the display of the link.

The full text article is available for purchase

$30.39 plus tax

 

OR

Back to top

Key:
Free Content - Free Content
New Content - New Content
Subscribed Content - Subscribed Content
Free Trial Content - Free Trial Content
Page Help Click here for Page Help
Shopping cart
Tools
Sign in






Need to register?
Sign up here
Text size: A | A | A | A