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| Journal of the New Zealand Medical Association,
21-May-2004, Vol 117 No 1194
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Rates of Chlamydia
trachomatis testing and chlamydial infection in pregnant women
Beverley Lawton, Sally Rose, Collette Bromhead, Selina
Brown, Jane MacDonald, and Jill Shepherd
Chlamydia
trachomatis (C. trachomatis) is
the most common bacterial sexually transmitted infection (STI) in New
Zealand.1 C.
trachomatis has a high rate of asymptomatic infection—approximately
80% of cases in females, and 45% in males, are estimated to be
asymptomatic.2
The exact prevalence of C.
trachomatis in New Zealand is unknown, although rates are typically
higher in females, in under 25-year-olds, and in Maori and Pacific
people.2,3 In 2000, a survey of laboratory and
STI clinic data in the Waikato and Bay of Plenty regions revealed an incidence
rate of 4162 per 100,000 for females aged
15–19.4
More recently, year 2002 laboratory data from Waikato and
Bay of Plenty reported increasing rates of C.
trachomatis—with up to 6998 cases per 100,000 for 15–19 year
old females.2 The overall rate of
C. trachomatis was reportedly five
times higher than that found in Australia (similarly calculated from laboratory
surveillance data).2 Dunedin laboratory figures
have also shown that the incidence of C.
trachomatis increased by 37% in females and 10% in males between March
2002 and March 2003.5
The prevalence of C.
trachomatis in females who were sexually active and provided a urine
sample for a New Zealand school-based study in Christchurch was
2.3%.6 Despite the apparent increasing
prevalence of C. trachomatis in New
Zealand, it is not a notifiable STI, there is no national data collection, and
there are no screening or treatment
guidelines.1
There are currently no New Zealand prevalence data for
C. trachomatis in pregnancy. Infection
rates reported in pregnant women in the USA and Canada have varied from 5% to
20%.7 The sequelae of untreated (which includes
undetected or asymptomatic) chlamydial infections can be severe—both for
the pregnant woman and for the neonate. Prenatal implications of chlamydial
infection for the mother and newborn include associations with ectopic
pregnancy, spontaneous abortions, preterm labour, amnionitis, premature rupture
of membranes, low birth weight, prematurity, still birth, and neonatal
deaths.7–9 Women with chlamydia during
pregnancy are also more likely to develop intrapartum fever and or late onset
postpartum endometritis after vaginal delivery.
It has been estimated that 20%–40% of infected
untreated women will progress to pelvic inflammatory disease
(PID)9—and these women will subsequently
be exposed to complications of infertility, chronic pelvic pain, ectopic
pregnancies, and death from ectopic pregnancy. For the newborn of untreated
mothers, inclusion conjunctivitis occurs in 11%–44% of cases, and
pneumonia occurs in 11–20% of cases.7
Furthermore, C. trachomatis in infancy
has also been associated with otitis media, bronchiolitis, pharyngitis, rhinitis
and gastroenteritis.8
Vertical transmission of
C. trachomatis to the neonate occurs in
approximately 50% of cases.8,10,11 During 2002,
up to 96 babies under the age of 12 months had
C. trachomatis diagnosed at Auckland
and Waikato/Bay of Plenty laboratories, which was an increase of almost 70% when
compared to 2001.2 By eliminating transmission
of chlamydial infection from mother to child, it has been shown there are more
favourable outcomes for both the mother and the newborn—including
significant reductions in premature labour, low birth weight, and increased
survival.9
Although screening for C.
trachomatis in pregnancy is considered best practice
internationally,12,13 there are currently no
guidelines in New Zealand advocating routine testing in pregnant women. Testing
for C. trachomatis is
desirable—for detecting and subsequently treating the chlamydial infection
in pregnant women, and for reducing the associated morbidity, which is
significant.
This audit process was carried out in a community medical
laboratory to determine the prevalence of C.
trachomatis testing and chlamydial infection in pregnant women who
delivered between 1999 and 2002.
MethodsEthics approval to carry out
this audit was granted by the Wellington Ethics Committee and consultation took
place with the Maori Health Directorate (Ministry of Health).
Crude
rates. Rates of
chlamydial infection were ascertained in all specimens (male and female) tested
at Wellington Medical Laboratory in 1999, 2000, 2001, 2002 (September to
September), and 2003 (September to June). Rates of chlamydial infection in
pregnancy (that may include both completed and terminated pregnancies) were
determined by matching all first antenatal bloods with
C. trachomatis tests in the same
laboratory in 1999–2003. The rate of C.
trachomatis in infants (1-year-old or younger) was determined by
retrieving results from all paediatric eye swabs tested during 2001, 2002, and
2003 (before 2001, data were not available for this type of test). This
laboratory uses the polymerase chain reaction (PCR) test (Amplicor CT/NG, Roche
Diagnostics) to routinely detect C.
trachomatis in both urine and swab samples.
Maternity care
provider data matched to laboratory tests. To determine the prevalence of
C. trachomatis testing in ongoing
pregnancies, details of completed pregnancies that were registered with a
maternity care provider were matched to laboratory data. For the years
1999–2002, name, date of birth, ethnicity and year of delivery were
identified for all women with completed pregnancies who were registered with a
maternity care provider.
Ethnicity was determined by self-identification using
the 2001 census form completed by patients at an antenatal hospital booking.
These data were forwarded to Wellington Medical Laboratory and matched with
patients who met one of three criteria: had a
C. trachomatis test; had a first
antenatal blood screen, or had a second antenatal blood screen at that
laboratory between 1998 and 2002. Data matching at the laboratory went back as
far as 1998 to capture pregnancies that began in 1998 and delivered in early
1999.
The laboratory assigned a study number to each patient,
and the anonymised data were returned to the research team for analysis. Data
included—study number; year of delivery; age at testing (under 25 years,
25 years and older); mean, median, and age-range of the sample; ethnicity;
whether tested for C.
trachomatis; and the outcome of
that test (whether positive or negative for C.
trachomatis).
ResultsCrude
rates. The (crude) rates of chlamydial infection in all male and female
specimens (ie, from antenatal specimens and in paediatric eye swabs tested at
the laboratory) are presented in Table 1.
Table 1. Prevalence rates of chlamydial infection in
all laboratory samples (male and female) tested between 1999 and 2003
*Includes both
completed and terminated pregnancies;
†n=5;
‡n=10;
§n=47.
Maternity care provider
matched to laboratory tests. The maternity care provider supplied the
laboratory with data for 7913 deliveries. Of those, 6614 matches were obtained
for women who had had an antenatal blood test through the laboratory—so we
could include them in the study sample. The 1299 women for whom no data was
available at the laboratory were excluded due to the possibility that they may
have been tested at another laboratory. The age range of the study sample was 14
to 52 years with a mean age of 30.6 years, and a median age of 31
years.
Tests for C. trachomatis
had been performed for 37.5% of the 6614 deliveries between 1999 and
2002. Of those tested, 4.8% were positive for
C. trachomatis, while 95.2% were
negative. Invalid results were obtained for two tests (Table 2).
When analysed by age when tested (under 25 years, 25 years
and older), the rate of testing for women 25 years and older (33.3%) was
significantly lower than for women under 25 years (61.7%) (p<0.0001). Of
those women tested, a significantly higher proportion of women under 25 years
tested positive for C. trachomatis
(12.2%) than those 25 years and older (2.3%), (p<0.0001).
Table 2. Rates of testing for
C. trachomatis in pregnant women (who
delivered between 1999 and 2002) and rates of chlamydial infection in those
tested
*Includes six
‘equivocal’ results, percentages calculated using denominator of all
those tested; †Includes
‘sole’ and ‘mixed’ Maori;
‡Includes all tests, including two
‘invalid’ results.
The rate of testing for C.
trachomatis during pregnancy differed significantly across ethnic groups
(p<0.0001), with testing in 59% of Pacific women, 54.9% of Maori women, and
32.5% of New Zealand European women. Of those tests that were carried out, the
percentage of those who tested positive for C.
trachomatis also differed
significantly by ethnic group (p<0.0001); 15.2% of Maori women, 12.5% of
Pacific women, 2% of New Zealand European women, and 0.5% of Asian women tested
positive for C. trachomatis.
Table 3 presents a model of estimated national rates of
C. trachomatis that have been scaled up
using the rates of testing and infection presented in Table 1. Figures were
calculated using the ethnicity-specific rates of testing and rates of chlamydial
infection for Maori, Pacific, and New Zealand European women, as well as 2001
national birth statistics for these ethnic
groups.14
Table 3. Model estimating national rates of
C. trachomatis in pregnancy, as well as
rates of undetected chlamydia in mothers and consequent infection in neonates
(based on the rates of testing and infection found in the present
audit)
*Ethnicity of the
mother giving birth; †Maximum number of
cases modelled using the number of births in 2001 and the ethnicity (all ages)
specific rates of chlamydia in Table 2;
‡Calculated by subtracting the number of
cases of detected chlamydia (calculated using ethnicity specific rates of
testing in Table 2) from the total estimated number of cases;
§Calculation based on 50% transmission
rate from estimated cases of undetected
chlamydia.
The estimated infection in the neonate was modelled from the
number of cases that would go undetected in pregnancy in the absence of testing,
half of which would be transmitted to the
neonate.8,10,11
DiscussionLess than half of all pregnant
women in this audit population were tested for
C. trachomatis between 1999 and 2002.
These results along with increased detection of chlamydial infection in New
Zealand neonates2 suggest that
C. trachomatis testing is not routinely
carried out in pregnancy in New Zealand.
The rate of C. trachomatis
in untested women is unknown, but the overseas evidence suggests that the
overall rate is likely to be similar to the rate in those
tested.7 The rate of chlamydial infection in
pregnant women (included in this audit) was high for Maori and Pacific women,
and for women under the age of 25 years. This finding was consistent with
previous New Zealand studies that have found a higher rate of infection in these
groups.2,3 However, there are limitations to
the interpretation of this data as other risk factors such as socioeconomic
status, previous STI, and educational level are not able to be taken into
account. Women in the present audit could all be considered
‘at-risk’ due to the fact that they had unprotected
intercourse.
The increasing incidence of chlamydial infection in the
community has been well documented, along with an increase in cases of neonatal
chlamydia.2,5 Table 3 attempts to quantify the
rate of possible undetected infection in New Zealand, as well as the subsequent
rates of infection in neonates using the rates obtained in this audit.
Furthermore, Table 3 shows an estimated 3485 women who gave birth in New Zealand
who might have been positive for C.
trachomatis. Indeed, based on ethnicity-specific testing rates, as many
as 1711 cases might have gone undetected, and with a 50% rate of vertical
transmission, up to 856 babies would have been infected with
C. trachomatis.
We recognise that estimating the burden of chlamydial
infection in this way has a number of weaknesses. The model does not take into
account variation in rates of testing, age at delivery, or the
ethnicity-specific variation in the age-structure of the population.
Furthermore, this model presumes the same rates of testing nationally, and
assumes that there will be an equal incidence of
C. trachomatis in those women who were
not tested. The median age of the mother at delivery in this sample (31 years)
was higher than the national average.14
Therefore, given the higher rate of C.
trachomatis in younger women, the rates reported here may underestimate
national rates of infection.
Diagnosis of maternal chlamydial infection requires either a
cervical or urethral swab, or first pass urine specimen. Recent recommendations
for the optimal diagnosis of C. trachomatis
infection include adding a urine sample to conventional swab(s) for
assessment, rather than replacing a swab with a urine
sample.15
While inhibition is a recognised problem with non-invasive
urine samples; when used in combination with swab(s), an increase in the
chlamydial detection rate of 9% has been
reported.15 It is recommended that high-risk
women are re-tested in the third trimester of their pregnancy to check for
re-infection.12 The recommended treatment for
pregnant women is erythromycin 500 mg by mouth (4 times per day, for 7
days).7
However, a major drawback of this treatment is the high rate
of gastrointestinal side effects and the length of treatment. Amoxycillin 500 mg
by mouth for 7 days is shown to be equal in efficacy to erythromycin, with fewer
side effects.16 Azithromycin 1 g is an
effective single dose treatment of C.
trachomatis, is listed as an alternative regimen when compliance is an
issue, and is being increasingly prescribed in pregnancy in New Zealand and
overseas.13,17 Contact tracing and treatment of
partners are also essential to prevent re-infection.
ConclusionsThere is a high rate of maternal
C. trachomatis and incomplete testing
for the infection in pregnant women. These findings highlight the need to
instigate routine testing for C. trachomatis
in pregnancy—to reduce the significant, yet preventable morbidity
associated with chlamydial infection in both the mother and the neonate.
Routine screening for C.
trachomatis in pregnancy is currently recommended in evidence-based
international guidelines,7,13 and has been
advocated by other researchers in New
Zealand.1,2,5 Pregnant women are an easily
reached population for testing and the beneficial health and economic
consequences of detecting and treating C.
trachomatis are significant.9 The
unacceptable rate of chlamydial infection in pregnancy, and the avoidable burden
of disease in pregnant women and neonates must be highlighted to maternity
caregivers.
Lastly, we recommend that testing for
C. trachomatis should be added to
best-practice screening that is already carried out in pregnancy.
Author information:
Beverley Lawton, Senior Research Fellow, Department of General Practice,
Wellington School of Medicine and Health Sciences, Wellington; Sally Rose,
Research Fellow, Department of General Practice, Wellington School of Medicine
and Health Sciences, Wellington; Collette Bromhead, Molecular Biologist,
Wellington Medical Laboratory, Wellington; Selina Brown, Senior Research Nurse,
Department of General Practice, Wellington School of Medicine and Health
Sciences, Wellington; Jane MacDonald, Clinical Director, Wellington Sexual
Health Services ; and Jill Shepherd, Board Member, Matpro (Wellington Maternity
Project), Wellington.
Acknowledgement: We
thank David Hall for his assistance with the Wellington Medical Laboratory
database.
Correspondence: Dr
Beverley Lawton, Aotearoa Women's Health Initiative, Department of General
Practice, Wellington School of Medicine and Health Sciences, PO Box 7343,
Wellington South. Fax: (04) 385 5473; email: bevlawton@wnmeds.ac.nz
References:
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