The importance of quality control of sputum smear microscopy: the effect of reading errors on treatment decisions and outcomes

SETTING: Ho Chi Minh City, Vietnam. OBJECTIVE: To evaluate the impact of slide reading errors at peripheral lev el on case-finding and treatment decisions. DESIGN: Over a 6-month period in 1997, information on date, type of slide, results of other slides from the patient, and treatment status was collecte d for all slides from district TB centers detected as having reading errors during smear microscopy quality control re-readings. RESULTS: Reading errors were detected in 117 slides: 115 (98.3%) were incor rectly read as negative, and 75 (65.2%) of these errors occurred in case-fi nding slides. In the 75 falsely negative case-finding slides, re-reading re sulted in initiation of treatment in 38 patients (50.7%). The remaining 37 (43.3%) had only one positive slide and were told to return for follow-up a fter 6 months; the two (5.4%) who did return were both diagnosed with activ e TB. Detection of errors in the 40 false-negative follow-up slides resulte d in treatment changes in four patients (10%). CONCLUSIONS: Quality control plays a critical role in helping to ensure the timely diagnosis and treatment of new TB cases and appropriate management of patients currently on treatment. The usefulness of quality control could be enhanced by focusing greater efforts on case-finding slides initially r ead as negative.