Detecting Chlamydia trachomatis by direct immunofluorescence using a Cytobrush sampling technique

Cervical sampling for diagnosis of genital chlamydial infection with a new brush device

OBJECTIVES

To compare a new sampling device, a brush, Accellone-Multi-Instrument (AMI), with a dacron-tipped swab for detection of Chlamydia trachomatis in endocervical specimens, and to evaluate if consecutive multiple cervical sampling as compared with such a single specimen would increase the sensitivity.

METHODS

501 females attending an STD clinic and 172 females attending a family planning clinic were examined prospectively. Two cervical specimens were collected from each woman. C trachomatis were detected by culture or enzyme immunoassay (IDEIA-III). Positive EIA samples were confirmed by a direct immunofluorescent test.

RESULTS

When cervical specimens were collected with the brush as the first device, 92% of the culture-positive cases were detected, and when the samples were collected with the dacron-tipped-swab first, 84% of the culture-positive cases were detected (p < 0.05). The first collected specimen detected 89% of the culture-positive cases and 81% of those that were positive by IDEIA.

CONCLUSIONS

The study indicates that the AMI brush is superior to non-toxic, dacron-tipped swabs for detection of C trachomatis in cervical samples by cell culture but not by ELISA, and that the sensitivity could be improved by analysing multiple cervical samples.

Laboratory techniques for the diagnosis of chlamydial infections

Yolk-sac inoculation of embryonated eggs was superseded 25 years ago by the use of cell cultures (often McCoy) for the isolation of Chlamydia trachomatis. Centrifugation of specimens onto the cell monolayers was shown to increase sensitivity, but little of late has further improved sensitivity which is at least ten-fold greater than that of eggs. However, culture is slow and labour intensive so that non-cultural techniques without these drawbacks have come to dominate. Direct fluorescent antibody (DFA) tests are rapid and have sensitivities that range from 70% to 100% for men and 68% to 100% for women, and specificities that range from 87% to 99% for men and 82% to 100% for women; if the tests are read by competent observers the values are at the top end of the ranges. The detection rate may be enhanced even further by relatively low-speed centrifugation of specimens before staining. Skilled reading is not a feature of enzyme immunoassays (EIAs) which according to the literature have sensitivities that range from 62% to 97% for men and 64% to 100% for women, and specificities that range from 92% to 100% for men and 89% to 100% for women. However, comparison against poor reference tests is responsible for most of the higher values and the clinician should not be misled into believing that EIAs have excellent sensitivity; the lower values in the ranges are closer to reality. Furthermore, EIAs that are being designed for use by general practitioners should be regarded with the greatest caution since lack of sensitivity means that chlamydia-positive patients will go undetected. The polymerase chain reaction (PCR) is not bedevilled by insensitivity but it is no more sensitive than the most sensitive cell culture or DFA tests. PCR is unsuitable for routine diagnosis but has a place as a research tool. For men, examination of "first-catch" urine samples by the best of the non-cultural procedures provides an acceptable non-invasive approach to diagnosis; for women, the value of examining urine may be less, but needs to be thoroughly tested. However, there is little doubt that a Cytobrush used to obtain cervical specimens holds no practical advantage over a swab. Serological tests are reliant on the provision of paired sera for making a diagnosis; high antibody titres in single sera may be suggestive of an aetiological association in deep-seated chlamydial infections (epididymitis, arthritis, salpingitis, etc), but unequivocal interpretation is unusual, particularly in an individual case, since the distinction between a current and past infection is problematical.

A comparison of cytobrush and cotton swab sampling for the detection of Chlamydia trachomatis by cell culture

A cytobrush was compared with a cotton-tipped aluminium shafted swab for the collection of 2024 paired endocervical specimens for the culture of Chlamydia trachomatis. There was no significant advantage with the use of either device with respect to the number of positive specimens detected or the number of inclusions present in positive specimens. However, the use of cytobrushes resulted in an increased level of cervical bleeding and increased collection of cervical mucus resulting in difficulties in the handling of laboratory specimens.