[An analysis on results of smear and culture of sputum from smear-positive tuberculosis patients].

OBJECTIVE

To study the positive rate of smear and culture in different sputa from smear-positive patients with tuberculosis, and to discuss the criteria of sputum selection for smear and culture.

METHODS

The results of smear and culture of sputum samples from 3813 cases during tuberculosis drug-resistance baseline survey in 2007 were retrospectively analyzed. The positive rates of smear and culture of spot sputum, night sputum and morning sputum were compared, and the culture positive rate of sputum samples with 1-2 acid fast bacilli (AFB)/300 fields was summarized. The χ(2) test was used for comparison.

RESULTS

The smear positive rate of spot sputum, night sputum, and morning sputum was 75.2% (2868/3813), 87.9% (3350/3813), and 89.4% (3408/3813) respectively. The percentage of cases which were positive for all the 3 sputum samples was 64.5% (2460/3813), while that for 2 samples and 1 sample was 23.4% (893/3813) and 12.1% (460/3813) respectively. The cumulative smear positive rate of spot sputum plus morning sputum reached 96.9% (3695/3813) of the rate combined from the 3 sputum samples. The culture positive rate of spot sputum, night sputum, and morning sputum was 97.8% (1654/1691), 96.7% (3006/3107) and 97.2% (2473/2543) respectively. For the smear positive cases, the positive rate of 2 sputum culture increased only 1.7% - 2.8% compared with that of 1 sputum culture. The culture positive rate of samples with a smear result of 1 - 2 AFB/300 fields was 90% (98/109).

CONCLUSIONS

When spot sputum and morning sputum are collected for the diagnosis, the number needed for smear can be decreased from 3 to 2. For smear-positive cases, if sputum is selected for culture according to the smear result, the number needed for culture can be decreased from 2 to 1. A smear result of 1 - 2 AFB/300 fields is of considerable diagnostic value for tuberculosis.