Chlamydia trachomatis is the most common bacterial sexually transmitted infection (STI) in Ireland [1]. The burden of genital C. trachomatis disease in Ireland is a major public health concern. In a previous study in the Mid-West of Ireland, the prevalence of chlamydia in men aged 17–35 attending an orthopaedic clinic and a university sports arena was estimated to be 5.9% [2].

In males, infection can manifest as urethritis or epididymitis, with complications such as Reiter's syndrome in those genetically predisposed [3,4]. Infection in women may present with urethritis, cervicitis, bartholinitis, or salpingitis and, if left untreated, the infection can become chronic and result in ectopic pregnancy, pelvic inflammatory disease and infertility [3].

Up to 70% of women and 50% of men with chlamydia infections do not show symptoms of the disease, resulting in a 'silent epidemic' [5,6]. Individuals unaware of their infection increase the risk of transmission of chlamydia in unprotected sexual contacts. Delays in seeking a diagnosis and treatment can result in increased transmission of chlamydia infection and its consequences. STI testing may be embarrassing for individuals and therefore those accessing diagnostic services may seek care outside their usual area of residence. Currently, there is no national chlamydia screening programme in Ireland. This study examines two sources of data on reported chlamydia and the origins of positive cases in the Mid-West of Ireland.

Methods and Materials

Two sources of data are available on genital chlamydia infections in the Health Services Executive (HSE) Mid-West: (a) data from the aggregate quarterly notifications of the free and confidential Sexually Transmitted Diseases (STD) or Genito-urinary Medicine (GUM) Clinics to the Department of Public Health; and (b) data on laboratory-confirmed infections from the Department of Medical Microbiology, Mid-Western Regional Hospital, Limerick. This laboratory performs all diagnostic chlamydia testing for the region covered by the HSE Mid-West, i.e. the counties of Clare, Limerick and Tipperary North. The region has a population of 339,591 (Census 2002), of which 214,402 are aged 15 to 59 years. STD/GUM services are not available in all regions of Ireland, and therefore cases of positive individuals outside the above catchment area may be included.

From March 2000 to December 2006, all laboratory-confirmed positive results were identified using one Nucleic Acid Amplification Technique (NAAT), i.e. ligase chain reaction (LCR) or polymerase chain reaction (PCR). From March 2000 to January 2004, the Abbott LcX (Abbott Laboratories, USA) was the diagnostic method used. It was replaced from January 2004 by the ABI Prism 7000 (Artus Hamburg GmbH) and Artus C. trachomatis PCR kit, which targets a region on the cryptic plasmid that is not affected by the deletion in the Swedish variant. The Microbiology Department at the Mid-Western Regional Hospital participates in an external Quality Control programme (National External Quality Assurance Scheme, NEQAS). Methods before 2000 were non-NAAT.

Data on all positive results for C. trachomatis were extracted from the Laboratory Information System of the Mid-Western Regional Hospital Microbiology Department and examined by sex and date of birth. While public health notification of chlamydia by laboratories became mandatory only in 2004, the data analysed here are comparable across all years as they are not based on public health notifications but on laboratory results. Duplicates, defined as two or more positive results on individuals with the same date of birth and sex within an interval of three months, and probable referrals (contemporaneous positive results from non-GUM/STD sources and GUM/STD Clinics, based on date of birth and sex) were excluded. Apparent re-infections, defined as two or more positive results more than three months apart were included. Duplicates and re-infections were classified as definite or probable based on the data available on each case. Codes used in STD/GUM services allow only date of birth and sex to be compared, therefore data may underestimate cases (where date of birth and sex are the same but the individual is different) and hence classification can only be probable. No data on sexual orientation was available in this dataset.

Results

Cases notified by STD/GUM clinics
Data reported by the STD/GUM Clinics to the Department of Public Health from 1998 to 2005 show a rising incidence of new chlamydia cases diagnosed from 1998 to 2002, and then a decline from 2003 to 2005 (Figure 1). Genital chlamydia infection was more common in women than in men in all years with the exception of 2000.

Laboratory-confirmed cases
There has been a steady rise in the number of requests for chlamydia testing in the HSE Mid-West over the last four years (Figure 2). Of 7,521 laboratory samples tested for chlamydia in 2006, 377 (5%) were GCT patient episodes. This percentage was consistent over the years studied (Table 1).

From January 2001 to December 2006, there were 2,328 laboratory-confirmed reports of chlamydia infections in total. Annually, there were up to between two and six cases of ocular chlamydia infections with a total of 26 cases over the period studied and these were excluded from the analysis. Also excluded were 215 'duplicates' or 'referrals' (129 definite and 86 probable), leaving 2,087 patient episodes of genital chlamydia infection. There were 213 cases classified as 're-infections' (84 definite and 129 probable) over the six-year period. Table 1 highlights the number of patient episodes of infection in men and women in the region from January 2001 to December 2006. In women there appears to be a steady increase in the number of genital chlamydia infections up to 2005 (Figure 2). The rate of infection in women is consistently almost twice the rate in men.

Young women (15 to 29 years) bear the greatest burden of disease in the region. Among those who sought diagnostic services, females aged 15 to 19 years were five times more likely to be found positive than males of the same age.

The median age of men at the time of infection was 25 years (Range: 16 to 56 years) and in women it was 23 years (Range: 15 to 53 years). The median age of women attending STD/GUM Clinic settings was 1.5 years younger than of women attending non-STD/GUM settings, although the overall age distribution for both men and women between STD/GUM and non-STD/GUM settings was similar.

General practitioners, family planning clinics (FPC) and hospital clinicians diagnosed 49% of chlamydia infections in the region. Females made up 65% of cases during the period 2001-2006. Of those cases diagnosed by non-STD/GUM clinics, 83% (856 of 1,027) were female, as shown by data from the HSE Mid-West (Table 3). This is markedly different from the data from STD/GUM Clinics, where similar numbers of males and females are seen and notified.

Discussion

Until recently, complete data on genital chlamydia infection in Ireland have been difficult to establish because there was significant under-reporting by clinicians outside the STD/GUM Clinics. Irish law places a statutory requirement on STD/GUM Clinics to provide aggregate quarterly STI data to the (regional) Medical Officer of Health in the Department of Public Health. The obligation to report cases of genital chlamydia infection was introduced for laboratories in 2004 and should allow a clearer assessment of the epidemiology of chlamydia infection in Ireland [7].

National data in Ireland, based on STD/GUM Clinic data, show an increase in the number of cases in Ireland, from seven per 100,000 population in 1995 to 86 per 100,000 in 2005 [1]. This is likely to be directly related to factors such as better surveillance methods, increasing incidence, greater awareness and screening, but also to more sensitive laboratory diagnostic techniques. Data on trends from the Mid-West are consistent with published data in other countries, with the rate of infection rising particularly in young women [8,9]. The lower rates in males may be due to infrequent contact with health services in general in contrast to females who attend for contraceptive advice, smear testing and pregnancy.

It is not appropriate to compare published data from national sources to data in this report, as only STD/GUM Clinic aggregate data are included nationally. Half of all chlamydia infection in the region is diagnosed by GPs, FPC and hospital clinicians (predominantly obstetric/gynaecology clinicians), with the remainder being diagnosed in regional STD/GUM Clinics. General practitioners and, to a lesser extent, hospital-based clinicians diagnose an increasing number of chlamydia infections, especially in women. Therefore general practitioners are in a position to offer opportunistic screening to women attending their practices given the increasing burden of infection in the community. One review suggests that women actively seeking health care are amenable to screening [10]. Under-reporting has a significant bearing on assessing the burden, surveillance and control of chlamydia infections in Ireland. This study in the Mid-West suggests that national data, which are based solely on aggregate returns from STD/GUM Clinics in Ireland, would underestimate the burden of chlamydia, more particularly the incidence in women. The data highlight those at greatest risk of chlamydia infection based on age and sex. With increasing numbers of diagnoses in the community, GPs and clinicians might consider targeting this group for opportunistic screening and sexual health advice. The large proportion of cases seen by clinicians outside STD/GUM Clinics, especially in the community, has implications for public health in terms of complete follow-up, partner notification and contact tracing. General practitioners should have access to ongoing education on STIs.

It was not possible to determine whether genital chlamydia positive cases diagnosed outside the STD/GUM Clinic setting were offered or received full STI screening. It appears that only a small number of such positive genital chlamydia cases are probably referred to the specialist STD/GUM service in the region (4%) indicating that management of the chlamydia infection in the non-STD Clinic setting was mainly by family doctors. The reasons for 're-infections' are unclear, and it is possible that a source of infection has not been identified and remains a reservoir for infection post-treatment. A debate on the need for a national chlamydia screening programme in Ireland, as introduced in other countries, is to be welcomed [11].

Acknowledgements

The authors would like to thank all the staff in the STD/GUM Clinic for the quarterly aggregate STI data. We acknowledge the work of all scientific staff in the Mid-Western Regional Microbiology Department who carried out diagnostic testing.