Evaluation of the serological response to syphilis treatment using an automated RPR test]

We evaluated the clinical usefulness of serological monitoring with an automated rapid plasma reagin (RPR) test in syphilis patients. Serum samples were obtained from 68 syphilis patients, including 57 cases infected with human immunodeficiency virus (HIV) from our clinic between February 2010 and May 2012. RPR titers were measured with both the conventional serial dilution manual method and the automated method before (baseline) and at several intervals after treatment. The criteria of a cure were defined based on RPR titers as equal to and/or more than a 4-fold decrease (with the manual method) or by RPR values lowered to the level of equal and/or less than 25% (with the automated method) within 6 months in comparison with baseline values. A serological cure was observed in 19 (95%) and 17 (85%) of the 20 cases with the manual method and the automated method after 6 months, respectively. For the other 3 cases, the RPR value ratios with the automated method were 25.4%, 25.9% and 37.9%. Among all 68 patients, 9 cases (13.2%) did not meet the criteria for a cure by both methods within 6 months, but all cases did within 12 months. The ratio of RPR values after several months against that of baseline was evaluated with a t-test; the RPR values with the automated method were significantly lower than those obtained with the manual method (p < 0.05), especially at 1 and 2 months (p < 0.01). The RPR value ratios of HIV-positive cases were significantly higher 1 and 2 months after (with the manual method) and 1 month after (with the automated method) than those of HIV-negative cases; however, no statistical significance was observed after 6 months between the RPR ratio of HIV-positive and HIV-negative cases. Based on these results, we infer that the RPR test with the automated method can be used in the same manner as the manual method for treatment monitoring of HIV-positive and HIV-negative syphilis patients, especially in the early phase of treatment.