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Abstract
Introduction Nucleic acid amplification tests, with their ability to detect very small amounts of nucleic acid, have become the principle diagnostic tests for Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (GC) in many sexual health clinics. The aim of this study was to investigate the extent of surface contamination with CT and GC within a city centre sexual health clinic and to evaluate the potential for contamination of containers used for the collection of self-taken swabs.
Method Surface contamination with CT and GC was assessed by systematically sampling 154 different sites within one clinic using transcription-mediated amplification (TMA), quantitative PCR and culture. The caps of containers used by patients to collect self-taken samples were also tested for CT and GC using TMA.
Results Of the 154 sites sampled, 20 (13.0%) tested positive on TMA. Of these, five (3.2%) were positive for CT alone, 11 (7.1%) for GC alone and four (2.6%) for both CT and GC. The proportion of GC TMA-positive test results differed by gender, with 11 (18.3%) positive results from the male patient clinic area compared with one (1.6%) from the female area (p=0.002). Positive samples were obtained from a variety of locations in the clinic, but the patient toilets were more likely to be contaminated than examination rooms (p=0.015). Quantitative PCR and culture assays were negative for all samples. 46 caps of the containers used for self-taken swabs were negative for both CT and GC on TMA testing.
Conclusions Surface contamination with chlamydial and gonococcal rRNA can occur within sexual health clinics, but the quantity of nucleic acid detected is low and infection risk to patients and staff is small. There remains a potential risk of contamination of patient samples leading to false-positive results.
- Contamination
- Chlamydia trachomatis
- Neisseria gonorrhoeae
- false positive
- NAAT
- AIDS
- genitourinary medicine
- gonorrhoea
- HIV
- sexual health
- chlamydia infection
- antibiotic resistance
- genital tract infect
- antimicrobial resistance
- Neisseria gonorrhoea
- LGV
- same day testing
- syphilis serology
- vaginal infections
- STD surveillance
- laboratory diagnosis
- statistics
- PID
- genitourinary medicine services
Statistics from Altmetric.com
- Contamination
- Chlamydia trachomatis
- Neisseria gonorrhoeae
- false positive
- NAAT
- AIDS
- genitourinary medicine
- gonorrhoea
- HIV
- sexual health
- chlamydia infection
- antibiotic resistance
- genital tract infect
- antimicrobial resistance
- Neisseria gonorrhoea
- LGV
- same day testing
- syphilis serology
- vaginal infections
- STD surveillance
- laboratory diagnosis
- statistics
- PID
- genitourinary medicine services
Introduction
Nucleic acid amplification tests (NAAT) have become the principle method of detection of Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (GC) from samples collected in many sexual health clinics. The National Chlamydia Screening Program that has been rolled out successfully throughout the UK also uses NAAT.1 ,2 The benefits of NA include high sensitivity and specificity and the potential for rapid throughput of samples.3 However, their ability to detect even very small amounts of nucleic acid increases the possibility of false-positive results, which in the sexual health setting can have far reaching consequences.
NAAT of patient self-taken specimens is widely used both within sexual health clinics and in community or outreach settings, and there is good evidence showing that the sensitivity and specificity of NAAT for the detection of CT and GC are maintained using self-taken samples.4 Despite the advantages of self-testing, there may be an increased risk of specimen contamination if chlamydial or gonococcal nucleic acid is present on clinic surfaces or on the hands of patients.
Contamination of patient samples can also occur within the laboratory5 ,6 and a false-positive result should be particularly considered where the test signal is borderline or the clinical history incompatible with the result obtained. False-positive results are not always a result of contamination but can also be due to the presence of non-specific amplification products related to suboptimal assay conditions or PCRs in which specificity may not be 100%.5 ,6
Previous studies have demonstrated a varying length of survival for CT and GC on inanimate surfaces. CT rRNA has been shown to persist for as little as a few days or as long as 50 days on a clinical bench6–8 and can be isolated from a variety of environmental sites within a sexual health clinic, including the examination room floor (88%), curtains (71.4%) and toilet areas—urinals (50%) and toilet seats (33%).6 The patient journey through a sexual health clinic will inevitably involve contact with equipment, furniture, toilet facilities and other communal areas. In addition, clinic staff may also be exposed to bacterial nucleic acid with the potential to cross-contaminate patient specimens. Studies in non-sexual health clinical settings have shown extensive contamination of computer keyboards and mobile phones in operating theatres with pathogens including coagulase-negative staphylococcus, diphtheria, micrococcus species and bacillus.9 ,10 Nucleic acid from organisms can also result in a positive NAAT, despite the organism being non-viable.11
Laboratory sources of contamination may also be relevant including contamination of laboratory reagents and equipment, in addition to carry over contamination from previous specimens.5 ,12 Contamination of adjacent samples following specimen leakage can also occur. Precautions in the laboratory to reduce contamination can include segregated areas for specimen preparation and testing, and hypochlorite cleansing as well as running an environmental swab with each specimen run.6
The aims of the study were to assess the extent and location of surface contamination with CT and GC in a sexual health clinic setting and evaluate the potential for contamination of containers used for the collection of self-taken swabs.
Methods
Molecular detection of CT and GC rRNA on clinic surface
Samples were taken from 154 environmental sites in a sexual health clinic in Birmingham, UK, including consultation rooms, examination rooms, patient toilets, sluice rooms, health advisor rooms, laboratory areas and venepuncture rooms (web appendix 1). Samples were taken from both male and female patient areas during afternoon and evening clinics after the areas had been used by patients. Cleaning practices were maintained throughout the period of sample collection, which were daily cleaning of the patient toilets by contracted cleaning staff using Sani100 and Lifeguard detergents, with hourly review of the clinical areas and cleaning by nursing staff with Clinell wipes after each patient.
The method for sample collection was standardised. Flat surfaces were wiped firmly with a swab three times diagonally from top to bottom and from left to right across the area of the surface to be tested. Door handles were swabbed with three diagonal strokes up and around the handle. Four samples were taken from each site. Samples were tested using APTIMA Combo 2 transcription-mediated amplification (TMA) assay to detect CT and GC rRNA, quantitative real-time PCR targeted at the CT cryptic plasmid, CT cell culture in McCoy cells (McCoy's 5A Medium (Modified) without Serum and with L-Glutamine) and GC culture directly inoculated onto New York City Media (an enriched selective media used for the isolation and cultivation of pathogenic Neisseria species). The relative light unit (RLU) values for each positive TMA specimen were recorded. APTIMA Combo 2 and GC culture were performed at Birmingham Childrens' Hospital laboratory, while the CT quantitative PCR and CT culture samples were sent to the Sexually Transmitted Bacteria Reference Laboratory for analysis.
Assessing potential contamination of self-taken swab containers
Forty-six previously tested self-taken TMA samples (both urine and vaginal swabs) were selected randomly. These included samples that were positive for GC and CT, CT alone, GC alone, negative and equivocal or indeterminate. The caps of the containers were sampled using a swab moistened in distilled water and wiped firmly over the outer edge of the cap for each patient specimen, with care taken not to make contact with the pierced section from the original test. Swabs were placed into APTIMA transport tubes prior to testing for CT and GC with TMA.
Statistical analysis
Data were recorded on an Excel spreadsheet and statistical analysis performed using IBM SPSS V.19.0.0. Rates of contamination were compared using Fisher's exact test, with Bonferroni-adjusted post-hoc pairwise tests, where applicable.
The project was assigned as a service evaluation and formal Ethics Committee approval was not sought.
Results
Of the 154 sites sampled, 20 (13.0%) tested positive on the TMA assay, with an additional seven equivocal and one indeterminate result. Five (3.2%) were positive for CT alone, 11 (7.1%) for GC alone and four (2.6%) were positive for both CT and GC. In total, 5.8% of surfaces tested positive for CT and 9.7% of surfaces tested positive for GC. Positive samples were obtained from most areas of the clinic including consultation rooms, examination rooms, patient toilets and sluice areas. Of the 22 positive results, six (27.3%) were from female patient areas, 12 (54.5%) were from male areas and four (18.2%) were from areas used by both male and female patients. The median RLU value of the positive results was 337 (IQ range: 237–671). All samples were negative on GC culture, CT culture and quantitative PCR for CT.
All 46 caps from the containers used for patient self-taken samples were negative for both CT and GC on TMA testing. Of the specimens in the containers, seven were positive for CT alone, six for GC alone and six positive for both CT and GC.
The rates of positive test results in the male and female sections of the clinic were compared, excluding areas of the clinic that were not exclusively used by either male or female patients. For CT TMA tests on the male patient area of the clinic, one (1.7%) returned a positive result that did not differ significantly from the five (7.8%) positive tests recorded from the female side of the clinic (p=0.209). The GC TMA test results differed significantly, with 11 (18.3%) positive results from the male clinic area compared with one (1.6%) from the female area (p=0.002).
Table 1 shows the proportion of positive samples for CT and GC in different areas of the clinic.
CT and GC transcription-mediated amplification (TMA) results in different clinic areas
A significant difference was observed in the positivity rate between samples taken in different clinic areas (p=0.003), and a post-hoc pairwise analysis showed a higher rate in the toilet area (22.2%) compared with the examination rooms (0%—Bonferroni-adjusted p=0.015).
No significant difference in the rates of GC on TMA testing was detected between different clinic areas (p=0.845).
Discussion
Surface contamination with chlamydial and/or gonococcal rRNA was identified in 13% of surfaces sampled within a sexual health clinic. Contamination was detected on surfaces used for the collection of clinical specimens (trolley surfaces, shelves, toilet flush handles) with the potential for contamination of clinical specimens. The majority of positive samples for GC (91.7%) were found in the male patient area (p=0.002). The only clinical areas not found to be contaminated were the health advisors' room and the clinic laboratory. Despite the detection of chlamydial and gonococcal rRNA using TMA, quantitative DNA and culture assays from the same sites were all negative.
The finding that GC contamination was found more often in the male clinic areas may reflect differences in methods of sample collection for men and women and a higher prevalence of GC in men attending the clinic. Male patients provide either urine samples, if they are asymptomatic, or urethral swabs taken by clinical staff if symptomatic. Female patients provide self-taken vaginal swabs if asymptomatic or cervical swabs are taken if they present with symptoms. Symptomatic patients are likely to have more genital discharge leading to a higher risk of environmental contamination, and splash contamination may occur when men provide urine samples. The higher ratio of male to female infections for GC in the clinic population (M:F ratio of 3:2 in 2011—data from clinic database) may also contribute to the higher rate of detection in the male patient areas.
Self-taken samples are obtained in the toilet areas, which may result in the higher rate of surface contamination with CT in these areas. Although patients are given instructions on sample collection, there is no direct monitoring of patients and it is not known how well these directions are followed.
The swabs, containers and their lids could potentially come into contact with contaminated surfaces or with hands/gloves that have been contaminated producing a false-positive test result. This risk may be higher for self-taken swabs when the patient is unfamiliar with handling swabs and containers. The negative TMA tests for GC and CT from containers and caps containing self-taken swabs suggest that extensive external contamination is not occurring even in the containers carrying positive specimens.
Studies have shown that routine disinfection or cleansing does not necessarily reduce bacterial contamination and may even seed the environment.13 ,14 Different cleansing agents have also been shown to have varying effectiveness, and wipes containing disinfectants were only shown to be superior to saline wipes when surfaces were wiped only once.15 Similarly, alcohol or nitric acid contained in commercial cleaning agents was shown to be ineffective at eliminating DNA when compared with irradiation, enzymatic treatments or solutions containing hydrochloric acid.5
In a study from Norwich,6 37.6% of swabbed surfaces tested positive for chlamydia compared to 5.8% in our study. The highest rates in the Norwich study were found on the floor, curtains and light fittings. It is not clear why this difference in detection rates occurred, although the clinic procedures and patient pathways are likely to differ between the two clinics and may be relevant. The number of samples taken in both studies were similar (117 and 154) and similar sites were sampled, although the floor and curtain contamination was not assessed in our study as they were considered to be at lower risk of causing false-positive results from patient specimens. Both studies used a Gen Probe assay, but our study used the APTIMA COMBO as opposed to the APTIMA. Gen Probe does not report any difference between the sensitivity and specificity of the two assays.16
Although we detected GC and CT nucleic acid, testing with culture and quantitative PCR was negative. This suggests that quantitatively the level of contamination was low and probably below that which could result in cross-infection. The low RLU values reported from positive specimens would support this (range 237–691) when compared with typical results seen in infected patients (95% >1000),14 although RLU values cannot be used to accurately quantify the amount of rRNA.
A limitation of the study is the small number of positive results, which limits further subanalysis. Further studies should investigate whether particular surfaces are more likely than others to be contaminated and the efficacy of different cleansing agents. Each sexual health clinic will also have its own systems and pathways that may affect which areas that are at highest risk of contamination. Our findings may suggest a benefit in regular monitoring of contamination of clinic areas in much the same way as laboratories do.
Our study has confirmed that surface contamination with chlamydial and gonococcal rRNA can occur within sexual health clinics. It highlights that different areas in the clinic are more prone to surface contamination than others and suggests that higher rates of GC contamination in the male areas of the clinic may be explained both by the method of sample collection and higher prevalence of infection in this group. The infection risk to patients and staff is considered to be low but the risk of contamination of patient samples leading to false-positive results remains possible, particularly in the context of self-taken swabs.
Key messages
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Surface contamination with chlamydial and gonococcal rRNA can occur within sexual health clinics.
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The quantity of nucleic acid detected is low and infection risk to patients and staff is small.
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There remains a potential risk of contamination of patient samples leading to false-positive results.
Acknowledgments
The authors would like to acknowledge the staff from the Birmingham Children's Hospital virology laboratory, the Sexually Transmitted Bacteria Reference Laboratory at the Health Protection Agency Centre for Infections, the Whittall Street Clinic including Rebecca Faville for their help with this project.
References
Supplementary materials
Supplementary Data
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Footnotes
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Competing interests None.
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Provenance and peer review Not commissioned; externally peer reviewed.