Survey with MMR remains as one of the most important methods available for measuring the size and extent of tuberculosis, specially in developing countries. Its value in case-finding programmes is well recognised. Nevertheless, mass miniature radiography with a single picture of the chest has a wide margin of error owing to the intra & inter-individual differences in X-ray reading. A study was undertaken to know the errors involved by repeating an X-ray picture after an interval of 3 to 4 months and judging the first picture in the light of a comparative reading of the two pictures. It is postulated that two pictures taken at an interval, may afford better judgement regarding the assessment of a case than a single picture only. A prevalence survey was carried out in Tumkur district in 1960-61, among 62 villages and 4 towns; 20 villages were selected for this study. A total of 8,000 persons were registered, 5,300 of them were X-rayed and re-read by two readers. Photofluorograms were repeated after three and a half months after the first picture. At the time of repeat X-ray, a spot sample of sputum was collected from persons with abnormal shadows.

Briefly the findings of the study were: (1) About 20% of bacillary cases were among those with inactive or non- tubercular shadows on the basis of a single X-ray film. (2) Inter-individual agreement for X-ray active cases was of the order of 50%. (3) Intra-individual agreement for X-ray active cases was 52% for one reader and 69% for the two readers. (4) Mass miniature radiography with a single film, in spite of its inherent limitations, is the best available method both for surveys as well as for case-finding programmes due to its ability to find cases as well as potential cases in a short time. (5) Even the agreement between two sputum samples collected within an interval of 1-3 days was 42% for positive results.

Limitations of a single X-ray picture for locating and interpreting shadows in the chest had been studied earlier. In order to reduce these limitations, it was suggested that two pictures of each person be taken where the second picture was to be taken after a vertical displacement of X-ray tube, up or down by about 4 to 5cms. The advantages of taking two pictures simultaneously as compared to a single picture have not been studied so far. Two mobile X-ray units each with an odelca camera were alternated for the single and double picture examinations. A total of about 2,000 persons were X-rayed and were read independently by 3 readers. A spot sample of sputum was collected 3-4 days later from persons with abnormal X-ray shadows and was examined by direct smear microscopy.

Comparison of the readings of the two sets of pictures did not show a better agreement between different (inter- individual) readers or between two different readings of the same reader (intra-individual) when the two picture technique was used. The X-ray cases detected by double picture only by any one reader were not confirmed, more often than those detected by single picture only. The X-ray pictures of the bacillary cases were also not interpreted more often as active tuberculosis by the two picture technique. It was concluded that the double picture technique does not offer any advantage over the single picture technique.