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Screening pulmonary tuberculosis suspects in Malawi: testing different strategies |
Harries A D, Kamenya A, Subramanyam V R, Maher D, Squire S B, Wirima J J, Nyangulu D S, Nunn P |
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Record Status This is a critical abstract of an economic evaluation that meets the criteria for inclusion on NHS EED. Each abstract contains a brief summary of the methods, the results and conclusions followed by a detailed critical assessment on the reliability of the study and the conclusions drawn. Health technology Screening pulmonary tuberculosis (PTB) suspects using two hypothetical strategies: (1) screen by sputum smear then chest X-ray (CXR) on smear negative patients, or (2) screen by chest radiograph then sputum smear on patients with CXR consistent with tuberculosis (TB).
Economic study type Cost-effectiveness analysis.
Study population Patients were aged 15 years or over and had been referred to the chronic cough room. The criteria for assessment were that TB suspects had had a cough for three weeks or more which had not responded to a course of antibiotics, and had experienced weight loss.
Setting Hospital. The study was carried out in Blantyre, Malawi.
Dates to which data relate Effectiveness data relate to the study conducted between February and October 1995. The costing of the two hypothetical strategies was based on a cost analysis of TB control activities in Malawi in March 1995. The price year was 1995.
Source of effectiveness data The evidence for the final outcomes was derived from a single study.
Link between effectiveness and cost data The costs were undertaken retrospectively and were based on the same sample as that used in the effectiveness analysis.
Study sample The initial study sample was appropriate for the clinical study question. The sample was taken from patients referred to the cough room from the out-patient department. Of the 1,127 patients identified, 427 fulfilled the criteria for being TB suspects. 11 were excluded from analysis because 3 sputum specimens were not submitted and 14 were excluded because routine chest radiographs were not available for viewing. The final sample consisted of 402 patients. No power calculations were reported in determining sample size.
Study design A case series study was carried out and the findings were fed into the two hypothetical strategies developed by the authors to establish what the outcomes would have been had they been adopted.
Analysis of effectiveness The basis for the analysis of clinical study (intention to treat or treatment completers) was not stated. The primary outcome was whether or not the patient had TB.
Effectiveness results In the cases selected, the sputum microscopy and culture results indicated that 111 (28%) of the patients were sputum smear positive and 213 patients (53%) were culture positive.
Of the 111 smear positive patients, 103 were culture positive and 8 were culture negative. Of the 291 smear negative patients, 110 (38%) were culture positive. Altogether 221 patients had smear and/or culture positive evidence of PTB.
In the chest radiography results in relation to sputum smear microscopy and culture of the 172 patients with a radiograph not considered to be PTB, 13 (8%) were sputum positive, 49 (28%) were sputum culture positive and 53 (31%) had smear and/or culture positive evidence of TB.
The comparison of the two hypothetical screening strategies indicated that 243 (60%) patients were diagnosed as having PTB. Of the 159 patients not diagnosed as having PTB, 40 (25%) had culture positive evidence of TB, and none were smear positive. In strategy B, 230 (57%) of the patients were diagnosed as having PTB. Of the 172 patients not diagnosed as having PTB, 53 (31%) had smear and/or culture positive evidence of TB, and 13 were sputum smear positive.
Clinical conclusions Adherence to strict clinical criteria for a TB suspect resulted in fewer patients requiring screening, a reduced workload, and a higher diagnostic sensitivity, both in terms of smear positive disease and radiological disease. The diagnostic efficacy of strategy B was less than that of A, and 13 smear positive patients were not correctly diagnosed. Both screening strategies raised concerns that a significant proportion of the patients with normal or minimally abnormal chest radiographs had smear or culture positive evidence of Mycobacterium tuberculosis.
Modelling No modelling was undertaken.
Measure of benefits used in the economic analysis The benefit measure was the number of properly identified TB cases.
Direct costs The direct costs considered were the cost of sputum smears and chest radiographs. The study was based on a provider perspective. The estimation of the number of tests carried out was based on actual data (number of patients), although the strategies under review were hypothetical. The estimation of costs of the two screening strategies was based on the cost analysis reported in the literature of TB control activities in Malawi in March 1995. No discounting was carried out due the short duration of the study. The quantities and costs were reported separately. The price year is assumed to have been 1995.
Statistical analysis of costs No statistical analysis was undertaken.
Indirect Costs The study was carried out from a provider perspective and indirect costs were not considered.
Sensitivity analysis No sensitivity analysis was carried out.
Estimated benefits used in the economic analysis In strategy A, 243 (60%) patients were diagnosed as having PTB. Of the 159 who were not diagnosed as having PTB, 40 (25%) had culture positive evidence of TB, and none were smear positive. In strategy B, 230 (57%) patients were diagnosed as having PTB. Of the 172 patients who were not diagnosed as having PTB, 53 (31%) had smear and/or culture positive evidence of TB; and 13 were sputum smear positive.
Cost results The total cost of strategy A was $1,124.7 and strategy B cost $1,251.1.
Synthesis of costs and benefits The cost per diagnosed case for strategy A was $4.63 and for strategy B, $5.55.
Authors' conclusions Although strategy B, screening first by chest radiography, resulted in a 43% reduction in sputum specimens requiring smear examination, the diagnostic efficacy was less and the costs were slightly higher compared with strategy A. Furthermore the chest radiography screening strategy resulted in 13 smear positive patients not being diagnosed. The authors indicated that there was concern with both screening strategies as a significant proportion of patients with normal or minimally abnormal chest radiographs had smear and/or culture positive evidence of Mycobacterium tuberculosis (particularly those found to be HIV positive).
CRD COMMENTARY - Selection of comparators The choice of comparator, representing as it did standard practice, was suitable for the study.
Validity of estimate of measure of benefit The estimate of measure of benefit was not explicitly stated, but it was implied to have been the reduction in the amount of laboratory workload and associated costs due to proper identification of patients with TB. The authors noted that they did not consider the specificity of each strategy which, if poor, would have resulted in false positive results with consequences for further tests. The improvement of the diagnostic accuracy, as highlighted by the authors, may allow the taking of one or two rather than three smears (this technology currently exists as cited in the paper).
Validity of estimate of costs The reporting of costs was appropriate as the costs/quantities were reported separately. However, the use of local rates and lack of sensitivity analysis limits the generalisability of the results.
Other issues The authors did not make any comparisons of their findings with similar studies, although the issue of generalisability was mentioned. The study enrolled people who had been identified as having, or who were suspected as having, TB and the conclusions were based on this group. The authors highlighted the limitations of their study, such as the fact that it did not address the question of diagnostic specificity.
Implications of the study The study endorsed the present strategy of screening first by sputum smear microscopy, as screening first by chest radiography did not correctly diagnose 13 of the patients. The study highlighted the need for educating outpatient staff to request sputum smear examinations for patients who fulfil the appropriate clinical criteria for being a TB suspect as one of the ways of reducing the heavy work load of the laboratory. The issues presented by patients who are seropositive for HIV were highlighted as a cause for concern in the methods used to identify TB patients. The authors indicated that further operational research was required in certain areas such as improving the diagnostic sensitivity of sputum smear microscopy by concentration methods.
Source of funding Financial support from the Global Tuberculosis Programme, World Health Organization, Geneva.
Bibliographic details Harries A D, Kamenya A, Subramanyam V R, Maher D, Squire S B, Wirima J J, Nyangulu D S, Nunn P. Screening pulmonary tuberculosis suspects in Malawi: testing different strategies. Transactions of the Royal Society of Tropical Medicine and Hygiene 1997; 91(4): 416-419 Indexing Status Subject indexing assigned by NLM MeSH Adolescent; Adult; Economics, Medical; Female; Humans; Malawi; Male; Mycobacterium tuberculosis /isolation & Radiography, Thoracic; Sputum /microbiology; Tuberculosis, Pulmonary /diagnosis; purification AccessionNumber 21998006074 Date bibliographic record published 31/10/2000 Date abstract record published 31/10/2000 |
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