Serological Monitoring of Infection Associated with Chlamydia Trachomatis in St. Petersburg
Published: 15.08.12 Updated: 15.08.2012 15:30:03
L.B. Kulyashova, L.A. Berezina, A.V. Zakrevskaya, A.B. Zhebrun
Federal State Scientific Institution “Pasteur Research Institute of Epidemiology and Microbiology”, St. Petersburg
Citation: Kulyashova LB, Berezina LA, Zakrevskaya AV et al. Serological Monitoring of Infection Associated with Chlamydia Trachomatis in St. Petersburg. EpiNorth 2011;12:109-13.
Chlamydia trachomatis infects reproductive organs. Data concerning the incidence of the urogenital chlamydiosis in Russia is incomplete. The purpose of this study is to investigate the prevalence of Chlamydia trachomatis among citizens of St. Petersburg.
A serological study of 2390 children and teenagers 0-18 years of age and 1843 adults 19-70 years of age was conducted. The data revealed a high level of chlamydial infection among new-born children and a rapid growth of the infection among teenagers. The results indicate that it is necessary to plan and take appropriate measures to prevent chlamydial infection among the population.
Urogenital chlamydiosis is one of the most wide-spread sexually transmitted infections [4, 5]. Women suffering from chlamydial infection may have tubal infertility and ectopic pregnancy or give birth to babies of lower than average weight . In Russia the disease started to be registered in 1994. Chlamydiosis belongs to the group of infections that are subject to mandatory statistical registration, which emphasizes the medical and social relevance of the pathology. Up to 100 cases of chlamydiosis per 100,000 population are registered in Russia every year , yet the statistical data do not correspond to the actual situation. This is due to the fact that the disease most often has an asymptomatic form, and until recently there have been no standardized diagnostic algorithms or any comprehensive registration system . There is no state monitoring program on chlamydial infection in Russia. Efficient prevention measures are difficult because there are still no objective data on disease prevalence caused by Chlamydia trachomatis among various population groups in St. Petersburg. An understanding of the epidemiology of the infection is of social and medical importance and can contribute to funding a solution for the demographical problems in the future. Thus, the goal of the study was to obtain information about the prevalence of Chlamydia trachomatis infection among citizens of St. Petersburg.
From 2008 to 2011, 2390 serum samples obtained from children and 1843 serum samples from blood donors of various ages who are living in St. Petersburg and Leningrad oblast were analyzed for post-vaccination immunity at the Pasteur Research Institute of Epidemiology and Microbiology.
Participants selected for the study had no diseases associated with the chlamydial infection at the start of the study and had not suffered from chlamydiosis or any other inflammatory urogenital diseases during the two previous years.
Chlamydia antibodies (IgG) were detected in serum samples by the enzyme-linked immunoassay (ELISA) method using the Chlamydia trachomatis-IgG-ELISA plus medac assay. This test system uses a synthetic peptide of a variable domain in the immunodominant segment of the major outer membrane protein (МОМP). Test results were assessed as follows:
- optical density (OD) of the blank <0.100
- average OD value of negative control <0.100
- OD value of positive control > 0.800
-”Cut-off ”= average OD value of negative controls + 0.340
- grey zone = ”Сut-off” ± 10%
The assay sensitivity according to the manufacturers’ evaluation is 94%, specificity 97%, reproducibility 94% and there are no false-positive results caused by cross reactions with other Chlamydiaceae family pathogens.
Statistical analysis was performed using parametric statistics. The relative values (frequency of positive results) and mean errors were calculated. The difference between the compared relative values was estimated by Student's t-test .
Information about the age of the study participants living in St. Petersburg and Leningrad oblast is given in Table 1.
Table 1. Age groups of the study participants (n=4233)
Statistics on positive test results from children’s samples in 2008-2011 is shown in Figure 1.
Fig. 1. Frequency of Chlamydia trachomatis serum antibodies detected by ELISA method among children of various age groups in St. Petersburg, 2008-2011
The analysis of Chlamydia trachomatis IgG antibodies showed a high level of seropositivity among the children less than 1 year of age (7.5% – 11.6%). Since the chlamydia antibodies were found in samples of new-born children during the first days after birth as well as of children over 6 months old, it is possible to conclude that the immunity in this age group was due to maternal antibodies or by transmission of the chlamydial infection during the perinatal period (children over 6 months).
In the age groups 1-5 and 6-11 years the seropositivity level was lower (4.3 – 4.8%) and appeared to correspond to the frequency of chronic chlamydial infection.
In the groups of teenagers the number of positive samples increased four and five times during the monitoring period reaching 17.8% in general, as compared to the results of children 1-11 years of age (P<0.01).
Analysis of test results among adults showed a high level of seropositive samples (11.2-22.0%) in all age groups (see Fig. 2), with an increase observed during 2010 and 2011 in the age group 19 to 29 years (17.4 – 32.5%).
Fig. 2. Frequency of Chlamydia trachomatis serum antibodies detected by ELISA method among adults in St. Petersburg, 2008-2011
The frequency of Chlamydia antibodies among men and women of various age groups is shown in Figure 3. The data demonstrate that in all age groups, specific antibodies among men (7.5%) were lower than among women (15.1%) (P<0.01).
Fig. 3. Frequency of IgG antibodies to Chlamydia trachomatis among men and women, 2008-2011
The results of sero-epidemiological tests conducted at the Pasteur Research Institute of Epidemiology and Microbiology within the last four years show a high level of Chlamydia trachomatis infection among persons in St. Petersburg and Leningrad oblast. IgG antibodies were detected in 7.5-11.6% of children under the age of 1 year indicating that they may suffer from the persistent chlamydial infection, which may cause inflammatory urogenital diseases in the future.
The high level of assay sensitivity and specificity indicated that the results should be accurate. Thus we have obtained information about the prevalence of chlamydial infection in various age groups and trends in the development of the infection through the results of laboratory analyses.
The data on the prevalence of chlamydial infection in all age groups of the population and the increase in disease incidence among children and teenagers contradict the official statistics. Thus it is necessary to develop a state program for prevention and treatment of the infection.
Common protocols with standardized laboratory diagnostic and monitoring methods may improve the surveillance of chlamydial infection. Such methods provide reliable information about the disease incidence and may be compared with information from other countries . The rapid growth of chlamydial infection among teenagers, which may cause various reproductive function pathologies in the future, makes it necessary to take active measures targeted at more effective prevention of the disease among this age group.
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