Confidence intervals for seroprevalence determined from pooled sera.

In population surveys of seroprevalence, it may not be most efficient to test all individual samples. The laboratory and statistical issues encountered when one first pools individual samples into groups of samples before laboratory analyses were discussed recently in relation to the seroprevalence of human immunodeficiency virus. In particular, point and confidence interval estimates for seroprevalence from pooled sera were derived. A potential problem with these confidence intervals is that they may contain negative values. This problem is most likely to occur in low-prevalence populations where pooling is most efficient. An alternative method of obtaining confidence intervals that cannot contain negative values is proposed and an example provided.