Letter to the Editor
To the Editor:
Ness et al1 recently demonstrated that bacterial vaginosis (BV) was common among a predominantly black group of women with concurrent gonococcal and/or chlamydial infection. However, the association between BV and subsequent, incident gonococcal and/or chlamydial infection was not significant.1 BV is associated with high vaginal pH. Studies in vitro demonstrated significant reduction of growth of Chlamydia trachomatis when exposed to acidic pH.2,3 It remains to be established whether the uptake of Neisseria gonorrhoeae and C. trachomatis in host cells in vivo is influenced by an increase in vaginal pH. We performed a prospective case–control study for a period of 12 months in a predominantly white population and found an association of high vaginal pH with gonococcal and chlamydial infection, even in the absence of BV.
The subjects were nonpregnant female subjects attending a genitourinary medicine clinic in Coventry, U.K., for sexually transmitted disease (STD) screening. Cases (n = 194) were confirmed diagnoses of gonorrhea and or chlamydial infection and the controls (n = 145) were attendees, consecutive to each gonorrhea and or chlamydial infection, whose result for STD screening was negative for any infection. All subjects underwent similar routine tests, which included tests for chlamydia, gonorrhea, Trichomonas vaginalis, candidiasis, and BV. The subjects with vaginal bleeding or with any discharge containing blood have been excluded because this can increase the vaginal pH independently. Subjects with vaginal bleeding resulting from bloody vaginal discharge or menstrual bleeding at the time of examination were excluded. Chlamydial infection was diagnosed with strand displacement amplification assay. Gonorrhea was diagnosed by microscopic examination of urethral and endocervical swabs and culture in modified New York media. Vaginal pH was measured by a standardized pH indicator tape (range, 3.0–8.0) on the day of the first examination and the collection was specified from the lateral wall of the vagina. This was preceded by removal of cervical mucus before obtaining the vaginal fluid. The measurement of vaginal pH has been done routinely in all the subjects on the first day of the examination when the diagnosis was unknown.
There were 137 females diagnosed with chlamydial infection, 44 with gonococcal infection, and 13 were infected with both infections. Most of the subjects were white (94%, Table 1), and cases were younger than controls (Table 1). Use of oral contraceptives was more common in subjects with chlamydial infection (Table 1). There was no difference in the use of condoms, history of previous STD, and time of LSI (Table 1). Twenty-four (12.3%) cases had BV. The median (range) pH of cases (5.0 [3.5–8.0]) compared with controls (4.0 [3.0–7.00]) was significantly higher (P = 0.001, Wilcoxon test). The number of subjects with pH 4.5 or above was higher among cases than controls (159 [81.5%] vs. 66 [45.0%], P = 0.001, χ2 test). There were 125 cases who did not have any other STDs and the median pH (range) of those (5.0 [3.5–6.5]) compared with controls (4.0 [3.5–7.0]) was higher (P = 0.001, Wilcoxon test). Similarly, the number of cases without any other STD whose median pH was 4.5 or above was higher among the cases than the controls (103 [83.4%] vs. 66 [45.4%], P = 0.001, χ2 test).
The vaginal pH may be increased in women in whom the vagina is colonized by a variety of facultative and obligatory anaerobic bacteria or other microbes such as in BV and T. vaginalis.5 However, even when the analyses were restricted to cases that did not have any other concurrent STD or BV, vaginal pH remained higher in the cases than in the controls. The association of high vaginal pH with concurrent gonorrhea and chlamydial infection, even in the absence of BV, in our study population compared with the study of Ness et al1 could be because of a diversity of the respective population.
The measurement of pH may not have been accurate, because it was done by eye estimation only. However, the measurement was performed on the day of first examination, when diagnoses were unknown, and thus any errors in pH measurement would not be expected to differ between cases and controls. Excess mucus secretion from the endocervix may have effect on vaginal pH. This study is unable to answer whether the rise in pH is the effect of chlamydial infection. Further study is needed to assess whether high vaginal pH is a cause or an effect of gonorrhea and or chlamydial infection.
1. Ness RB, Kip KE, Soper DE, et al. Bacterial vaginosis (BV) and the risk of incident gonococcal or chlamydial genital infection in a predominantly black population. Sex Transm Dis 2005; 32:413–417.
2. Mahmoud EA, Svensson LO, Olsson SE, et al. Antichlamydial activity of vaginal secretion. Am J Obstet Gynecol 1995; 172:1268–1272.
3. Yasin B, Pang M, Wager A, et al. Chlamydia trachomatis
infection in environments mimicking normal and abnormal vaginal pH. Proceedings Fourth meeting of the European Society for Chlamydia Research, Helsinki, Finland, August 2000:296.
4. Schramm N, Bagnell CR, Wyrick PB. Vesicles containing Chlamydia trachomatis
serover L2 remain above pH 6 within HEC-1B cells. Infect Immun 1996; 64:1208–1214.
5. Chen KCS, Forsyth PS, Buchanan TM, et al. Amine content of vaginal fluid from untreated and treated patients with non-specific vaginitis. J Clin Invest 1979; 63:828–835.