Effect of storage of sputum specimens at room temperature on smear and culture results.

A study of 41 specimens of sputum stored for up to 28 days at room temperature in a tropical country showed that smear results were not affected by storage, the positivity being 83% before storage and 80-83% after. The culture positivity was 88% before storage, and 83%, 68%, 22%, 13% and 0% after 3, 7, 14, 21 and 28 days of storage respectively. The reduction in positivity on storage attains significance at 7 days (P = 0.05). Another study involved 163 specimens of sputum and storage for 3, 5 or 7 days. Each specimen was examined before storage and after 2 periods of storage, at random. The smear results were again not affected. There was, however, significant loss of viability, the proportion culture positive being reduced from 92% before storage to 83% at 3 days (P = 0.05), 71% at 5 days (P less than 0.01) and 63% at 7 days (P less than 0.001). The contamination rate was 5%, 7%, 12% and 18% respectively. It is concluded that sputum should not be stored at room temperature for longer than 3 days for culture but it can be stored for 4 weeks without any loss of smear-positivity.