A total of 66 subjects with a clinical diagnosis of BV on the initial visit, as confirmed by positivity for all four Amsel criteria, were initially enrolled in the study. Of these, 32 subjects did not meet the inclusion criteria for the study and were excluded from the final analysis. The reasons for exclusion were as follows; 27 subjects did not return for either of the scheduled follow-up visits 7 or 14 days after the initial visit (classified as loss to follow-up), which we speculate occurred because of a lack of adequate incentive once the condition had been treated. Four subjects did not meet the entry criteria (one did not have a full record of results according to the Amsel criteria, one was pregnant, and two were using an antifungal or antimicrobial medication), and the sample from one subject was not analyzed by OMA due to an instrument failure.
Of the remaining 34 subjects, 24 completed both of the follow-up visits in the prescribed time frame. The data for 10 subjects who were able to return for at least one of the follow-up visits were also included. All of these patients had completed the course of treatment. The majority of subjects examined were African-American (94%) and had an average age of 29 years (maximum age, 45 years; minimum age, 18 years).
The results for the subjects included in the study are listed in Table . It shows how the level of acetic acid for each subject varied during the treatment phase (i.e., between days 1 and 7) and the recovery phase (between days 7 and 14) of the study. Table also shows patient status for the clinical diagnosis of BV (on the basis of the Amsel criteria) and the Nugent scores for each patient visit, together with any concurrent infections. Note that the values presented for acetic acid concentrations are single-point measurements because only one patient swab was available for analysis with OMA. The estimated 95% confidence intervals for each patient can be determined by calculating the value ±15.6%.
Acetic concentrations, clinical diagnosis, and Nugent scores for the patients included in the studya
A box-whisker plot of the acetic acid response for each sample analyzed is shown in Fig. . The box has horizontal lines at the lower quartile, median, and upper quartile values, which were calculated for the day 1, day 7, and day 14 data sets. The whiskers are lines extending from each end of the box to show the 2.5 and 97.5 centiles. For the day 7 and the day 14 data sets, a number of points plotted outside the whiskers. Typically, for a normally distributed data set these would be described as outliers, but in this instance they reflect the fact that the distributions of acetic acid are skewed. A previous study (Evans et al., submitted for publication) has shown that the distribution of acetic acid in non-BV patients approximates the lognormal distribution. It should be noted that three of the sample points from Table were excluded from the box-whisker plot (i.e., patient 60 for day 7, patient 11 for day 14, and patient 54 for day 14) because for these three patients the clinician determined by use of the Amsel criteria that the BV had not resolved, which agreed with the results obtained with OMA.
Box-whisker plot of study data, including the 900-ppm acetic acid concentration threshold for the diagnosis of BV.
It is evident from the box-whisker plots that, after treatment with metronidazole, on day 1 BV-positive swab samples show much lower levels of acetic acid than swabs taken from the same patient before treatment. Furthermore, the results demonstrate that the acetic acid marker threshold (i.e., 900 ppm) used by the OMA-BV device to determine whether a sample is BV positive or negative holds true in this study.
By using the calculated acetic acid concentrations, the diagnosis of BV status was determined with OMA for each sample. The agreements between the results obtained with OMA and those obtained by use of the Amsel criteria and the Nugent system are summarized in Table .
Agreements between the results obtained by OMA and those obtained by use of the Amsel criteria and the Nugent classified resultsa
There was excellent agreement between the results obtained by use of the Amsel criteria and those obtained with OMA, with disagreements between the tests for only 2 of the 92 samples with which both tests were performed (i.e., 98% agreement).
Typically, a Nugent score of 7 or greater is defined as being consistent with BV and a Nugent score of 3 or less is indicative of normal flora. A score between 4 and 6 is indicative of an “intermediate” flora. In this study the samples with intermediate results according to the Nugent scoring system were classified as BV negative to reflect the common belief that a Nugent score of 6 or less does not necessarily correlate with BV (23
) and should not be interpreted to be consistent with incipient BV. Note that none of the samples from the patients scored intermediate on the initial visit, while the samples from three patients scored intermediate on days 7 and 14 (see Table for details). This simplifies comparison with the binary outcome of the test with OMA. The overall correlation between the test with OMA and the Nugent scoring system was also very good, with disagreement of the results for only 5 of the 90 samples with which both tests were performed (i.e., 94% agreement).