• Open Access

Chlamydia trachomatis in Tasmania 2001–2007: rising notification trends

Authors


Correspondence to:
Nicola Stephens, Communicable Diseases Prevention Unit, Department of Health and Human Services, GPO Box 125, Hobart, Tasmania 7001. Fax: (03) 6222 7744; e-mail: nicola.stephens@dhhs.tas.gov.au

Abstract

Objectives: To investigate trends in notification rates of Chlamydia trachomatis in Tasmania, Australia, by population sub-groups, from 1 January 2001 to 31 December 2007.

Methods: An enhanced surveillance dataset was used to supplement case notifications. Rates based on age group were analysed by sex, geographic region, indigenous status, sexual exposure, reason for testing and healthcare provider.

Results: In all age groups, the notification rate increased steeply. The highest rates were seen in the ages 15–24 years; this age group represented 15% of the population but accounted for 74% of the chlamydial notifications. The increased rates in females aged 15–24 years and males 15–19 years in Tasmania were larger than the increases observed nationally. Rates were consistently higher in urban areas. Females were more likely to have been tested as a result of screening, and males were more likely to have been tested when presenting with symptoms or as a result of contact tracing. The majority of cases reported sexual exposure with opposite sex partners only.

Conclusions: This study highlights the increasing significance of chlamydial infection as a public health issue, the gender differences in health-seeking behaviour, and the discrepancies in testing patterns. These findings will assist with the design of health promotion programs.

Genital infections with Chlamydia trachomatis (chlamydia) are a major cause of disease and morbidity internationally, and a steady rise in rates has been recognised in the past two decades.1,2 The World Health Organization (WHO) estimates that the global disease burden for treating chlamydia patients is $10 billion per year.3

In Australia, chlamydia is the most common sexually transmissible bacterial infection4 and the rate of notifications has increased each year since surveillance of the condition commenced in 1991.5,6 Nationally, notification rates have been consistently highest in the age groups 15–19 years and 20–24 years, and these two age groups have also experienced the steepest increases in notification rates over time.

Between 2001 and 2007 in Australia, the notification rates in females aged 15–19 years rose from 568 to 1,348 cases per 100,000 population, and in females aged 20–24 years the notification rates rose from 667 to 1614 cases per 100,000 population. In males aged 15–19 years, notifications rose from 149 cases per 100,000 population in 2001 to 387 cases per 100,000 population in 2007, and for males 20–24 years the rates increased from 375 to 991 cases per 100,000 population.7

The costs of chlamydia infection for the Australian healthcare system have been estimated to be between $90 million and $160 million per year.8 Chlamydia infection can lead to significant health complications, including pelvic inflammatory disease, endometritis and ectopic pregnancy in women, and epididymitis and reactive arthritis in men.2,9–11 Chlamydia can also result in infertility in both males and females.12–15 A large proportion of chlamydia infections are asymptomatic1,8 and as a result often remain undiagnosed, increasing the likelihood of health complications9–11 and adding to the spread of infection.16

Screening has been recognised as a cost-effective method of reducing the prevalence of chlamydia,8,17–19 and chlamydial infection meets the WHO criteria for a screening program.8,20 The Australian Government's National Sexually Transmissible Infection Strategy 2005–200821 identified chlamydia as a priority and as a result the Australian Government plans to implement systematic screening and testing in the general population. Who to screen, how often, in what setting, and type of screening program are all questions still under debate.19,22–24

Although chlamydia is a notifiable disease in all Australian States and Territories, Tasmania is the only jurisdiction to conduct follow-up on all notified cases for the purpose of collecting enhanced data. Smaller studies have shown that enhanced surveillance can provide valuable epidemiological information useful in focusing chlamydia control efforts8,25 and in defining the burden of chlamydia in the Australian community.6 Since 2005, enhanced STI surveillance data has been collected nationally for gonococcal infection, donovanosis and syphilis,26 and the enhanced data collected on chlamydia in Tasmania is fully compatible with the data collected nationally for those infections.

Our study analyses the unique dataset collected on chlamydia infections in Tasmania and provides a statistical comparison of rates in population sub-groups observed over the time period January 2001 to December 2007.

Methods

Case definition

For the purposes of this study, a case was defined as a person with sexually acquired, laboratory confirmed Chlamydia trachomatis (chlamydia) infection with specimen collection date from 1 January 2001 to 31 December 2007 inclusive. Cases with ocular infections were excluded. Cases with a laboratory confirmed test for Chlamydia trachomatis within the previous four weeks were also excluded. Laboratory evidence was defined in accordance with the Communicable Diseases Network of Australia guidelines27 as:

  • isolation of C. trachomatis from cell culture;
  • detection of C. trachomatis by nucleic acid testing; or
  • detection of C. trachomatis antigen.

Data collection and management

We identified our cases from the Tasmanian Notifiable Diseases Database (TNDD) held within the Communicable Diseases Prevention Unit (CDPU) in the Department of Health and Human Services (DHHS), Tasmania. Laboratories are obliged under the Public Health Act Tasmania 1997 to provide core data on all laboratory-confirmed cases of chlamydia to the CDPU29 and treating clinicians were actively followed up by the CDPU for collection of the Tasmania-specific enhanced data by a standard one-page mailed questionnaire (Table 1). All notified laboratory data was entered into the TNDD in preparation for reporting to the Commonwealth Department of Health and Ageing, and the Tasmanian enhanced data collected from clinicians was entered into a separate area of the TNDD created for the NNDSS STI surveillance dataset.26 Data collected before 2005 was retrospectively coded and entered into the enhanced dataset.

Table 1.  Data collected on Chlamydia trachomatis infection in Tasmania.
Data Notified by LaboratoriesData Collected from Clinicians
Disease codeConfirmation of case's sex
Laboratory nameIndigenous status
Laboratory numberReason for testing the patient – symptomatic or asymptomatic
Specimen collection dateIf asymptomatic, reason for testing
Surname – first two initials onlyWhether case reports sexual contact with:
 a. person(s) of the opposite sex;
 b. person(s) of the same sex;
 c. person(s) of both sexes;
 d. unknown
First name – first two initials only
 Past history of chlamydial infection, if yes, year(s) of previous infection(s)
Date of birthWhether assistance with contact tracing is required
SexWhether case reports undertaking commercial sex work within the past twelve months
Region of residence in Tasmania
Any further comments
Name of treating clinician
Site of infection

Analysis

Rates of notifications based on age group were analysed by sex, geographic region, indigenous status, sexual exposure, reason for testing and healthcare provider. Healthcare provider data was coded by one of the authors (DC), using pathology laboratory reports, the data collected on clinical facility type, and an up-to-date database of clinicians held within the TNDD.28 The geographical classification system was based on the Australian Standard Geographical Classification system (Australian Bureau of Statistics).30 For analyses, cases classified as rural or regional were categorised as non-urban cases, and cases classified as metropolitan were categorised as urban cases.

Population denominators were derived from the estimated resident population of each collection district obtained from the Australian Bureau of Statistics by sex and five-year age groups for each year of data collection (2001–2007). Seven age groups were used for the analyses: 10–14 years, 15–19 years, 20–24 years, 25–29 years, 30–34 years, 35–39 years and 40+ years.

Data were extracted into a Microsoft® Excel spreadsheet and analysed using Stata® version 10.0 (Stata Corporation, College Station, TX, US) (Stata). Exposures were expressed as dichotomous variables and crude rate ratios (RR) with 95% confidence intervals (CI) were calculated.

Results

Incidence

Between 1 January 2001 and 31 December 2007 inclusive, there were 5,072 cases of chlamydia notified in Tasmania of which 99.6% (n=5,053) were isolated by nucleic acid testing with the remainder (0.4%) detected by antigen testing. The number of notifications increased steeply each year from 2001 to 2007 in both males and females.

The 1,116 notifications received in 2007 represented an increase of 202% over the number of reported cases in 2001 (n=369). Female notifications accounted for 67% of all cases (Figure 1). Enhanced data was collected for 85% of notified cases (n=4,301) with a response rate consistent with the core notification data set by both gender and age group.

Figure 1.

Chlamydia notifications Tasmania 2001–2007 by sex.

The median age of female cases was 20 years (range 13 to 61 years) and the median age of male cases was 23 years (range 14 to 69 years). In cases aged less than 30 years, female notifications greatly exceeded male notifications. Eighty per cent of female cases (n=2,717) were aged between 15 and 24 years. This age group of female cases made up 54% of the total of all notifications received over the study time period. Sixty-two per cent of male cases were aged between 15 and 24 years (n=1,041).

Notification rates by age groups

In all age groups, the notification rate per 100,000 population increased steeply over the period 2001 to 2007. In age groups under 35 years, in both sexes, the increases were significant.

The highest rates for both sexes were seen in the age groups 15–19 years and 20–24 years. Between 2001 and 2007, persons aged 15–24 years represented 15% of the Tasmanian population,30 this same age group accounted for 74% of the Tasmanian chlamydial notifications.

Between 2001 and 2007, the notification rate for females in the 15–19 year age group increased by 1,127 cases per 100,000 population (195%, p<0.01), and the rate in females aged 20–24 years increased by 1,086 per 100,000 population (167%, p<0.01). In males, increases of 287 per 100,000 population (15–19 year age group) (228%, p<0.01) and 472 per 100,000 population (20–24 year age group) (126%, p<0.01) were observed.

Notification rates by urban/non-urban status

The rate of chlamydia notifications per 100,000 population was consistently higher in urban areas than in non-urban areas. The rates for males and females in both geographic categories increased steeply over the seven-year period 2001 to 2007. Urban rates increased by 213 cases per 100,000 population for females and by 109 cases per 100,000 population for males; and non-urban rates increased by 239 cases per 100,000 population for females and 107 cases per 100,000 population for males (Figure 2).

Figure 2.

Rates of chlamydia notifications per 100,000 population, by urban status and sex Tasmania 2001–2007.

Indigenous status

Data on indigenous status was collected for 71% (n=1196) of male cases and 68% (n=2319) of female cases. Two per cent reported Aboriginal or Torres Strait Islander origin. Notification patterns were found to be the same as in the general population.

Commercial sex work

Data on whether the case reported undertaking commercial sex work within the 12 months prior to infection with chlamydia was received for 532 (32%) of notified male cases and 1077 (32%) of notified female cases. One male case and nine female cases were reported as having undertaken commercial sex work during that time period.

Reason for testing

Females were more likely to have been tested for chlamydia infection as a result of screening, and males were more likely to have been tested for chlamydia when presenting with symptoms or as a result of contact tracing (Table 2).

Table 2.  Reason for testing by sex, Chlamydia trachomatis notifications Tasmania 2001–2007.
Reason for testingFemales (n=2,894)Males (n=1,408)
Symptomatic presentation1,081 (37%)737 (52%)
Contact tracing376 (13%)455 (32%)
Screening1,437 (50%)216 (15%)

Sexual exposure

The majority of cases reported sexual exposure with opposite sex partners only. Cases aged 35 years and older were more likely to report sexual exposure with same sex partners and less likely to report opposite sex partners than the younger age groups (Table 3).

Table 3.  Sexual exposure by age group, Chlamydia trachomatis notifications Tasmania 2001–2007.
Sexual exposure10–14 yrs (n=23)15–19 yrs (n=962)20–24 yrs (n=1,105)25–29 yrs (n=390)30–34 yrs (n=141)35–39yrs (n=75)40+ yrs (n=73)
Opposite sex only22 (96%)929 (97%)1,064 (96%)363 (93%)133 (94%)64 (85%)62 (85%)
Same sex only0 (0%)30 (3%)40 (4%)24 (6%)8 (6%)10 (13%)8 (11%)
Both sexes1 (4%)3 (0%)1 (0%)3 (1%)0 (0%)1 (1%)3 (4%)

Healthcare provider

Most cases were diagnosed by a general practitioner, however females were significantly more likely than males to be diagnosed through a public hospital (RR 1.2; 95% CI 1.1–1.3) or a family planning clinic (RR 1.4; 95% CI 1.3–1.4), and less likely than males to be diagnosed through a general practitioner (RR 0.8; 95% CI 0.8–0.8) or sexual health clinic (RR 0.7; 95% CI 0.7–0.8) (Table 4).

Table 4.  Type of healthcare provider by sex, Chlamydia trachomatis notifications Tasmania 2001–2007.
Type of healthcare providerFemales, n (%)Males, n (%)
General Practice2425 (71%)1399 (84%)
Family Planning Clinic409 (12%)40 (2%)
Sexual Health Clinic197 (6%)192 (11%)
Public hospital156 (5%)35 (2%)
Private hospital3 (0%)4 (0%)
Private obstetricians/gynaecologists212 (6%)0 (0%)

Discussion

Our study is the first in Australia to provide a comparison of chlamydia notification rates by subgroups derived from a population-based enhanced dataset collected over a seven-year period, with a valid high response rate.

We found the majority of notifications were in people aged 15–24 years, with an over-representation of females in this age group. This peak can be interpreted in a number of ways including, greater utilisation of healthcare by females of this age, targeted and opportunistic testing within the cohort, and a cohort with high susceptibility to infection. Our results highlight the need for targeting safer sex interventions for this age group.

As chlamydia is equally transmitted in males and females,6 our data suggests both significant under-screening and under-reporting in males. Strategies to improve screening in men need to be developed and continues to be an area in need of further research. Unlike females, males do not routinely consult a doctor about their sexual health and contraception31 unless symptomatic or alerted through partner notification systems. Awareness within general practice and emergency departments32 of opportunistic screening of males who present acutely for other reasons would help boost screening, particularly given the ease of screening based on urine sampling. In general, however, males, particularly healthy young males in the age groups at most risk, access healthcare infrequently. The Australian Institute of Health and Welfare has found that males visit doctors consistently less than females,33 therefore it would be advantageous to consider extending screening into non-medical settings, such as sporting clubs, as proposed by Gold et al.34

Notification rates in males were highest in the cohort of 20–24 year olds and may be illustrative of the concept of age bridging.35 Age bridging in this context is when a male has a female sexual partner who is two or more years younger. Jennings et al.35 found that this group of males often had multiple partners in short timeframes and were likely to use drugs and alcohol in relation to sexual intercourse. The available enhanced data from Tasmania does not confirm this behaviour but suggests a further area of research.

The 2009 Guidelines for preventive activities in general practice from the Royal Australian College of General Practitioners (RACGP) suggests that all sexually active females aged under 25 years, and all sexually active people aged 15–25 years with a recent change in sexual partner or with a pattern of inconsistent or no condom usage, should be screened for chlamydial infection every 12 months.36 Concentration on the under 25 year old females is reinforced by the Tasmanian dataset.

The increase in notification rates in Tasmania in females in the age groups 15–19 years and 20–24 years and in males in the age group 15–19 years were larger than the increases that have been observed nationally.7 This would suggest that systematic screening in Tasmania should encompass people in the age range 15–24 years, however jurisdictional differences may necessitate States and Territories establish tailored screening programs based not only on notification rates but also on rigorous modelling of potential strategies.

The finding that older cases were more likely to report sexual exposure with same sex partners may reflect a real difference across age groups, or a reluctance of younger cases to disclose their sexual history to their treating medical practitioner. If disclosure is an issue, this has implications for effective contact tracing. Patient referral is used for almost all contact tracing,37 and patient reluctance has been found previously to be the most common barrier to contact tracing for sexually transmitted infections.38

Although the majority of cases had their infection diagnosed through a general practitioner, the range and the differences between the sexes and across age groups in choice of healthcare provider highlights the importance of the availability of a variety of services. This is particularly relevant to ensure that type of healthcare provider does not become an obstacle to testing for young people at highest risk of infection.39

Of note from our data is the small number of notifications that have come from hospitals. Chlamydia is associated with adverse pregnancy outcomes such as risk of pre-term delivery and premature rupture of the membranes40 and puerperal infections.41 The RACGP suggests chlamydial screening be considered for pregnant women who are considered to be at increased risk.42 Chen et al.43 recent study supports this recommendation. They found that 72% of the infections detected in their study would have been found if screening had been restricted to all women under 20 years of age and all women aged 16–25 years who reported more than one sexual partner in the previous 12 months. While some of the general practice notification figures may represent antenatal screening, the lack of hospital-based notifications highlights the need to consider routine chlamydia screening in hospital-based antenatal settings, particularly in the cohorts aged 15–24 years and those reporting more than one sexual partner.

We detected consistently lower notification rates of infection in non-urban areas, a pattern observed elsewhere.2 Our finding warrants further investigation, as it is not known whether it reflects inequitable access to chlamydia testing, a difference in health-seeking behaviours, or a true difference by geography.

The type and sensitivity of diagnostic tests was constant over the study time period and, therefore, was unlikely to have influenced the increase in notification rates. Increased notifications could, however, be related to increased testing17 and an exploration of the testing effort over the time period of the study is needed to assess this association.

Excluding cases with a confirmed test within the previous four weeks point minimised the risk of including retests. Hosnefeld et al.44 conducted a systematic review of the literature that examined reinfection with chlamydia and gonorrhoea and found that, in all but two of the studies included, reinfection was defined as a positive test greater than two weeks after an initial positive. In Australia, the Reinfection Period Convention Project conducted in New South Wales, developed conventions for reinfection periods based on best available evidence. The project found that 30 days after primary infection with chlamydia was the appropriate time period for subsequent positive diagnoses to be considered new episodes of infection.45

A limitation of our study is that enhanced data was not collected for 15% of cases. However, there was no difference found in the age, sex or geographical location of the cases for whom we collected enhanced data and for whom we did not, and therefore the risk of selection bias is minimal.

The majority of notifications reported in our study were based on tests conducted as a result of symptomatic presentation or screening and as a large proportion of chlamydial infections remain asymptomatic, it is likely that our notification rates are an underestimation of the true rates. A formal epidemiological population-based prevalence study in Tasmania would allow a more accurate assessment of the rates and provide further evidence to inform planning of appropriate health services.

Acknowledgements

The authors wish to thank the staff from the Communicable Diseases Prevention Unit for their diligent work, including data entry of the notification and surveillance data, the staff of the Sexual Health Service for their assistance and input, Tasmanian pathology laboratory staff, and the healthcare providers who assisted us with enhanced data. Thanks also to Professor Graeme Jones for his helpful comments on the manuscript and to Dr Stephen Quinn for his statistical advice.

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