PROCEDURES FOR DEVELOPING A SIMPLE SCORING METHOD BASED ON UNSOPHISTICATED CRITERIA FOR SCREENING CHILDREN FOR TUBERCULOSIS

OBJECTIVE: To develop a scoring system for screening children for tube rculosis (TB) and for selecting suspects for further investigation in tuberculosis control programmes. Application of the score model, which would not require sophisticated or expensive technology, would be dir ected towards resource-poor countries with high prevalences of tubercu losis, where health care workers have to deal with diagnostic problems away from district hospitals or diagnostic facilities. DESIGN: Based on contributions from members of an IUATLD task group from 10 countrie s on the use of diagnostic criteria in childhood tuberculosis, criteri a were selected to be used as elements in a score model. Data were col lected by standardised questionnaire on 879 subjects aged under 15 yea rs, Of these, 794 were considered probable or confirmed cases of tuber culosis by the diagnosing doctors. From each record, the criteria/proc edures used in the diagnosis of probable/confirmed TB and regarded by the doctors as relevant criteria were selected. Bacteriology, histolog y and chest radiography were used either singly or collectively as the definitive reference (gold standard) against which the more subjectiv e criteria (symptoms, clinical signs, skin test) would be evaluated. T he latter criteria cited as relevant were then ranked and further expl ored for inclusion in the score model. The relative importance of each criterion to every other criterion on the list was expressed as weigh ts, determined by employing a logarithmic least squares method to solv e the ratio scale estimation problem which underlies decision-making i nvolving more than one criterion. The resultant values were then assig ned to each criterion in the final score model. RESULTS: The five clin ical criteria thought to be most relevant as predictors of disease in children were history of contact with a case of tuberculosis, positive skin test, persistent cough, low weight for age, and unexplained/ pro longed fever. In selecting the optimal cut-off points for the model at which tuberculosis would be suspected, low sensitivity and specificit y (below 70%) but reasonably good positive predictive values (60%-77%) were obtained, depending on age group and epidemiological setting. In low tuberculosis prevalence settings, heavy reliance is placed by the model on a history of contact with a household case of tuberculosis a nd on a positive skin test, both of which have to be true. For high pr evalence settings, more or less equal weighting is assigned to all fiv e elements. Case contact and skin tests are less important, with low b ody weight, prolonged fever and cough being more indicative of tubercu losis. CONCLUSION: The model provides for epidemiological differences between target populations and should prove successful as a screening tool to select children for further investigation by radiography and b acteriology.