Cycles in seroprevalence to
serovar Pomona in California sea lions stranding in northern California. Three panels correspond to (a) total seroprevalence (titers ≥ 1:100), (b) low-titer seroprevalence (titers ≥ 1:100 and <1:800), and (c) high-titer seroprevalence (titers ≥ 1:800). Solid lines show estimates derived from a random sample of all stranded sea lions, including those judged to have stranded due to leptospirosis. Dashed lines show estimated seroprevalence after leptospirosis strands are removed from the dataset. Isolated points in 1992 and 1993 show estimates derived from non-randomized samples from an earlier publication (18). Error bars show 95% confidence intervals.