Chlamydia

Antenatal care provides opportunities for testing women from population groups with a high prevalence of chlamydia infection.

40.1 Background

Chlamydia is caused by the bacterium Chlamydia trachomatis. Chlamydia infection is asymptomatic in at least 70% of women. In women, chlamydia initially infects the cervix and urethra, eventually causing abnormal vaginal discharge and dysuria (Silva et al 2011). Untreated, the infection can reach the fallopian tubes, causing pelvic inflammatory disease and adhesions. In pregnant women, chlamydia may affect normal intra- and extrauterine development (Silva et al 2011).

40.1.1 Prevalence of chlamydia

Rates of diagnosis

Chlamydia is the most frequently reported sexually transmissible infection in Australia. The notification rate was relatively stable between 2011 and 2015 and increased by 13% between 2015 and 2017 (Kirby Institute 2018a). Notifications have been higher in women than in men in all years (441.8 vs 349.9 per 100,000 in 2017). In 2017, the rate in the Aboriginal and Torres Strait Islander population was 2.8 times that in the non Indigenous population (1,193.9 vs 427.0 per 100,000), increasing to five times higher in remote/very remote areas (Kirby Institute 2018b).

Age 

Among women, rates in the 15–19 year age group have declined (from 2302.0 in 2011 to 1,772.8 per 100,000 in 2017), rates in the 20–24 year age group have remained stable (2,226.7 in 2011 and 2,346.0 in 2017) and rates in the 25–29 year age group have increased (from 927.8 in 2011 to 1,111.4 per 100,000 in 2017) (Kirby Institute 2018a). In 2017, rates among Aboriginal and Torres Strait Islander women aged 15–19 and 20–29 years were 3.8 times and 2.7 times higher, respectively, than in the non-Indigenous population (Kirby Institute 2018b).

Geographical distribution

Between 2013 and 2017 in New South Wales, there was a 30% increase in chlamydia notification rates from 289.9 to 377.5 per 100,000 (Kirby Institute 2018a). Similarly, in Queensland there was a steady increase from 437.8 to 488.4 per 100,000. Between 2016 and 2017, notification rates increased by 9% in New South Wales and by 8% in South Australia and Victoria. Notification rates of chlamydia have been highest and remained stable in remote and very remote regions in the 5-year period from 2013 to 2017 (824.6 per 100,000 in 2017) (Kirby Institute 2018a). Notification rates increased by 20% in major cities in the same period (335.8 to 403.4 per 100,000 in 2017), but declined by 5% in inner and outer regional areas (407.2 to 398.9 per 100,000).

40.1.2 Risks associated with chlamydia in pregnancy

A systematic review of cohort studies (Silva et al 2011) found that chlamydia infection during pregnancy was associated with an increased risk of preterm birth (RR 1.35; 95%CI 1.11 to 1.63), low birth weight (RR 1.52; 95%CI 1.24 to 1.87) and perinatal mortality (RR 1.84; 95%CI 1.15 to 2.94). There was no clear evidence of an increased risk of premature rupture of membranes (RR 1.13; 95%CI 0.95 to 1.34), miscarriage (RR 1.20; 95%CI 0.65 to 2.20) or postpartum endometritis (0.89; 95%CI 0.49 to 1.61).

40.2 Chlamydia testing

The Australian STI Management Guidelines recommend nucleic acid amplification testing (NAAT) of first pass urine, endocervical, vaginal or anorectal swabs (if the woman has anal sex or anorectal symptoms) and advise consideration of self-collection of samples by pregnant women ASHA 2018.

40.2.1 Diagnostic accuracy

No recent studies were identified that explicitly compared a diagnostic test to a reference test among pregnant women with uncomplicated pregnancies. Identified studies found that:

• sensitivity and specificity for chlamydia of urine samples relative to endocervical samples were 96.5% (95%CI 90.1 to 99.3%) and 100% (99.8 to 100%) and positive and negative predictive values were 100% (95%CI 95.6 to 100%) and 99.8% (95%CI 99.5 to 100%) Roberts et al 2011
• while pregnant women specifically have not been studied, the results available in non-pregnant populations are encouraging for the ability to test and treat women in antenatal care using point-of-care tests Herbst de Cortina et al 2016.

40.2.2 Availability of effective treatment

A cohort study found that, compared to women whose chlamydia infection was detected after 20 weeks or persisted during pregnancy, women whose chlamydia was detected and treated before 20 weeks gestation had a reduced risk of preterm birth in the less than 20 year age group (RR 0.54; 95%CI 0.37 to 0.80) but there was no clear difference in risk for women in other age groups Folger 2014.

40.2.3 Cost-effectiveness

An Australian cost-effectiveness study Ong et al 2016 found that, from an Australian Government perspective, chlamydia testing for all women aged 16–25 years old during an antenatal visit was likely to be cost-effective compared with no testing or selective testing, especially with increasing chlamydia prevalence (the study assumed a prevalence of 3%; in 2016 prevalence was 1.9% among women aged 15–19 years, 2.4% among women aged 20–24 years and 1.1% among women aged 24–29 years).

International cost-effectiveness studies found that:  

• universal antenatal testing for chlamydia was cost-saving in the Netherlands (estimated overall prevalence 3.9%), with further increases in savings when testing was targeted to pregnant women younger than 30 years of age Rours et al 2016
• cost and benefit of universal testing in pregnancy in the United States was reliant on the prevalence of chlamydia — when prevalence was above 16.9% there were net cost savings; at a prevalence of 8%, expenses were $124.65 million ($19.34/individual); and at a prevalence of 6.7%, net expenditure for screening was $249.08 million ($38.65/individual) Ditkowsky et al 2017.

40.3 Routine versus targeted testing

No recent studies were identified that directly compared outcomes associated with universal antenatal testing with those associated with targeted or no testing. However, the evidence supports testing of young Australian women at the first antenatal visit based on:

• the high prevalence of chlamydia in young people in Australia and the increase in notifications among women aged 25–29 years (see Section 40.1.1)
• early treatment reducing the risk of preterm birth among young women (see Section 40.2.2)
• the cost-effectiveness of antenatal screening among women aged 16–25 years (see Section 40.2.3)
• the benefits of consistency between recommendations in national guidelines (eg (ASHA 2018; RACGP 2016)).

In areas of high prevalence, repeat testing may be required.

40.3.1 Uptake of testing recommendations

An Australian study that assessed clinical uptake of the RANZCOG 2006 recommendation to test women younger than 25 found that, in 2010, only about one-fifth of participants routinely offered testing to women in this population group Li et al 2013. The study highlighted the need for national clinical leadership regarding testing for chlamydia among pregnant women. Current RANZCOG guidance is to selectively test women based on local prevalence RANZCOG 2016.

40.4 Treatment of chlamydia

The recommended treatment for chlamydia in pregnancy is oral azithromycin 1g as a single dose ASHA 2018. Testing for other sexually transmitted infections for women with diagnosed chlamydia is also recommended.

40.5 Practice summary: chlamydia

When: At the first contact with women younger than 30 years

Who: Midwife; GP; obstetrician; Aboriginal and Torres Strait Islander health worker; multicultural health worker

• Discuss chlamydia
  Explain the association between chlamydia and preterm birth and low birth weight, that tests for the infection are available and that it is easily treated with antibiotics.
• Take a holistic approach
  If a woman tests positive for chlamydia, important considerations include counselling, contact tracing, partner testing, testing for other sexually transmitted infections and follow-up. Any positive tests should be notified to public health.
• Learn about locally available resources
  Available testing services and support organisations will vary by location.

40.5 Resources

• ASHA (2018) Australian STI Management Guidelines for Use in Primary Care. Australasian Sexual Health Alliance. 
• HIV Medicine">ASHM (2016) Australasian Contact Tracing Guidelines. Australasian Society for HIV, Viral Hepatitis and Sexual Health Medicine.
• Palasanthiran P, Starr M, Jones C et al (2014) Management of perinatal infections. Sydney: Australasian Society for Infectious Diseases (ASID).