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Genital chlamydial infection in South Australia: review of testing and notification data for the period 1991-2000.

In this quarterly report a review of genital chlamydial data collected in South Australia over a decade highlights the impact of developments in medical technology during the period. These data demonstrate the usefulness of monitoring testing practices as a component of routine surveillance of sexually transmitted diseases.

Introduction

Since the early 1970s, Chlamydia trachomatis (immunotypes D through to K) has been recognised as a genital pathogen.1 In men, genital chlamydial infection commonly causes urethritis with possible complications of epididymitis, infertility and Reiters syndrome. In women, infection may produce a cervicitis with the potential sequelae of salpingitis and subsequent risk of infertility, ectopic pregnancy or chronic pelvic pain.2 Asymptomatic infection is common in both sexes.
Genital chlamydial infection is sexually transmitted, usually through vaginal intercourse. Occasionally it is transmitted by oral and anal sex. Chlamydia can be transmitted from mother to child during birth, causing conjunctivitis or pneumonia in the neonate. Genital chlamydial infections are prevalent worldwide.

Notification of genital chlamydial infection

Since 1988, genital chlamydial infection has been designated a notifiable disease under the South Australian Public and Environmental Health Act, making laboratory and medical reporting of cases to Sexually Transmitted Diseases (STD) Services a legal requirement.

Incidence and prevalence

During the decade 1991 to 2000, STD Services received 9376 notifications of genital chlamydial infection; 3669 (39%) cases occurred in males and 5707 (61%) in females. In 1996 an increase in reported cases coincided with the introduction of DNA amplification technologies such as polymerase and ligase chain reactions (PCR, LCR). Since 1996 the reported incidence has remained stable, with a range of 1001 to 1050 cases per year (Figure 1).

The true prevalence of genital chlamydial infection in South Australia is unknown. Available data are likely to underestimate the actual prevalence as many infections are asymptomatic and may go undiagnosed. Sentinel data are available from Clinic 275, the South Australian STD clinic, where all clients are offerred testing for genital chlamydial infection. Between 1991 and 2000, of 18206 males and 11864 females tested during their first clinic attendance, Chlamydia trachomatis was detected in 4.3% of men and 4.8% of women (Table 1). However, clinic attendees may not be typical of the Adelaide metropolitan population.

In the Anangu Pitjantjatjara Lands in the far North-West of South Australia, the Nganampa Health Council conducts annual, community-wide screening programs for STDs. In the year 2000, 71% of the population aged between 12 and 40 years were screened, with 3.9% of participants testing positive for Chlamydia trachomatis.3

Table 1. Chlamydia yields in first time attendees at Clinic 275.

Annual number of tests performed, cases diagnosed and percentage yield 
of positive tests, by sex.

Trends in testing and diagnosis of Chlamydia trachomatis.

Genital chlamydial infection is best diagnosed from a urethral swab in males or a cervical swab in females. Since the introduction of PCR testing, detection of Chlamydia trachomatis in urine specimens has facilitated diagnosis of infection in asymptomatic males and in females where collection of a cervical swab is impractical.

PCR technology is suitable for the testing of specimens collected some distance from laboratory facilities and permits less invasive methods of specimen collection such as urine testing. Between 1995 and 2000, the proportion of females diagnosed by PCR testing of urine specimens rose from 4% to 27% of cases. In males, diagnosis by detection of Chlamydia trachomatis in urine increased from 25% to 60% of cases for the same time period.

A high proportion of tests continue to be performed on women (Table 2).4 The female to male ratio of tests performed fell from 4.1:1 in 1995 to 3.1:1 in 1996, and has decreased only slightly since 1996 (Table 2). The female to male ratio of cases diagnosed has remained constant since 1991 with an average ratio for the decade of 1.6:1 (Table 2).

Between 1991 and 1995, the number of notified cases of genital chlamydial infection in females equated to 2% of tests performed. For the period 1996 to 2000 this proportion rose to 2.7%. The yield in males has remained stable over the decade with notified infections equating to an average of 5.1% of tests performed (Table 2).

Table 2. Laboratory testing for genital chlamydial infection.

Annual number of tests performed, cases diagnosed and percentage 
of positive tests by sex, and, annual female to male testing ratio and case ratio.

^{* These percentages are not adjusted for the fact that some clients may have had more than one positive test.}

Source of notification

During 1995 and 1996, female cases of genital chlamydial infection diagnosed by general practitioners (GPs) increased from 246 to 436 per year. Since 1996, this number has declined marginally, with GPs diagnosing about two thirds of all female cases each year (Figure 2). In males, the number of cases diagnosed by GPs also rose in 1996, with a further slight increase in the latter half of the decade (Figure 3).

An increase in notifications from the Nganampa Health Council of the Anangu Pitjantjatjara lands in 1996 coincided with the introduction of annual STD screening programs (Figures 2 & 3). In the year 2000 program, the Nganampa Health Council trialed the use of self-collected vaginal swabs by one community of women within the Anangu Pitjantjatjara lands.

Demographic Characteristics

The characteristics of age, racial origin and likely location of infection have remained stable throughout the decade.

Persons under twenty five years represented between 47-55% of male cases, and
69-76% of female cases per annum (Table 3). Surveillance data on rates of disease in specific age groups supports the view that genital chlamydia is more prevalent in young adults. However, this data is likely to be affected by testing biases such as the current testing ratio of 2.8 females to every male, and variation in the likelihood of being tested amongst different age groups (Table 4).

Between 1991 and 2000, 82% of notified cases were Caucasian (Table 3). The proportion of cases assigned to each racial group is a reflection of varying testing practices within these groups. For all racial groups, the annual number of notifications increased after the introduction of PCR testing, then remained stable between 1996 and 2000.

Eighty six percent of men and ninety two percent of women acquired the infection in South Australia (Table 3).

Table 3. Summary statistics: notifications of genital chlamydial infection,

South Australia 1991 to 2000.

^{* Age not recorded for 6 cases}

^{# Location is not recorded for 54 cases, 13 of which were reported from Central Australia}

Table 4. Genital chlamydial infection, 1/1/2000 - 31/12/2000.
Rate per 100,000 population, by age group and sex.

^* Australian Bureau of Statistics 1996 census data.⁶

Symptomatology

The association between genital chlamydial infection and clinical symptoms is often unclear. Many clients present with asymptomatic infection or, their apparent symptomatology may be caused by other factors such as co-infections.

Sentinel data is available on cases diagnosed at Clinic 275. Of 830 females and 1243 males identified as having genital chlamydial infection between 1991 and 2000, 270 (33%) females and 565 (45%) males were noted to have discharge and / or dysuria.

Repeat infections

Between 1991 and 2000, 220 (6%) males and 363 (6.3%) females were notified with two episodes of genital chlamydial infection. Ninety people (1%) were notified with more than two infections.

Summary

Throughout the decade 1991 to 2000, surveillance of genital chlamydial infection in South Australia has been affected by changes of testing practices by both laboratories and medical officers. In particular, the introduction of PCR testing, capable of detecting Chlamydia trachomatis in both genital swabs and urine specimens, may have been responsible for an increase in the annual number of notifications in 1996. These testing procedures have facilitated screening of persons living in remote areas, and are likely to have brought about increased testing amongst the male population.

These data do not support changes in the actual incidence or prevalence of genital chlamydial infection in South Australia between 1991 and 2000. Demographic data including age, racial origin and likely location of infection have remained stable throughout the decade.

References

1. King K Holmes et al, editors. Sexually Transmitted Diseases (Third edition). McGraw Hill. 1998.
2. James Chin, editor, Control of Communicable Diseases Manual (Seventeenth edition). American Public Health Association. 2000.
3. Nganampa Health Council. Annual Report 1999/2000. Alice Springs.
4. STD Control Branch. Sexually Transmitted Diseases in South Australia, Epidemiologic Reports 5-12, 1991 - 1998. Public and Environmental Health Service, Department of Human Services. ISSN 1033-0607. www.stdservices.on.net/publications
5. STD Services. Sexually Transmitted Diseases in South Australia, Epidemiologic Reports 13 & 14, 1999, 2000. Internal Medicine Service, Royal Adelaide Hospital. ISSN 1033-0607. www.stdservices.on.net/publications
6. Australian Bureau of Statistics. 30 June 1996. Catalogue No 3235.4, released March 1998.

Bernadette Kenny
STD Services
September 2001.

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