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Seroprevalence of Anti-tetanus Antibodies in Women attending Omdurman Maternity Antenatal Clinic in Sudan

Salma A. Elmahdi1, 2*, Khalid H. Bakheit1 and Ahmed M. Musa3
  • 1 Faculty of Medicine Khartoum University , Department of Bichemistry, Sudan
  • 2 Sudan Federal Ministry of Health, Sudan
  • 3 Institute of Endemic Diseases Khartoum University, Department of Clinical Pathology & Immunology, Sudan

Abstract
Background: Sudan is one of 39 countries which have yet to eliminate maternal and neonatal tetanus (MNT). Vaccination with tetanus toxoid (TT) provides immunity against tetanus. There are adequate published data regarding vaccination coverage, however, there is no matching data concerning the serological levels of anti tetanus antibodies among pregnant women in Sudan.
Objectives: To assess immunization against tetanus in terms of seroprevalence of anti-tetanus antibodies, its relationship-if any- with age, gravidity, number of TT doses, and time elapsed since last vaccination.
Patients and methods: Thirty-nine pregnant women consented to participate and were randomly included in the study. A commercially available indirect enzyme-linked immunosorbent assay (ELISA) kit was used to measure serum antitetanus antibody levels among the study group. Based on the kit, concentrations of ≥ 1.0, 0.15 – 0.99 and < 0.15 IU/ml were interpreted as full protection, basic protection and susceptibility respectively.
Results: The overall rate of full protection was found to be 69.2%. The concentration of antitetanus antibodies was significantly associated with the vaccination status (p value = 0.00), number of TT doses (p value = 0.01). The longer the time elapsed since the last TT dose the more susceptible the individuals are to tetanus (p value = 0.00). No significant association with either age or gravidity.
Conclusion: Vaccination achieved satisfactory levels of antitetanus immunity, thus adherence to vaccination schedules should be promoted. However, booster doses may be needed.
Introduction
Maternal and neonatal tetanus (MNT) continues to pose a major health concern locally, regionally and globally, particularly so in the developing countries [1, 2]. In 1988, the world health organization (WHO) estimated that 787,000 newborns died of neonatal tetanus (NT); this dropped to 59,000 by 2008 thus a 92% reduction from the situation in the late 1980s. By 2008-the last year from which estimates are available- 39 countries have yet to eliminate MNT, Sudan being one of them [3].
MNT elimination is defined as less than one case of neonatal tetanus per 1000 live births at district level [3]. MNT employs vaccination with tetanus toxoid (TT) containing vaccines as a core strategy. In Sudan, TT is provided for pregnant women as well as children as part of a nationwide vaccination policy [4]. However, vaccination rates by themselves are not enough to judge the level of population’s protection, as they do not take into account the true biological level of immunity [5, 6]. There are adequate published data regarding vaccination coverage in Sudan, but there is no matching publications concerning the serological levels of anti tetanus antibodies among Sudanese women.
Antibodies that develop following vaccination confer immunity against tetanus [7]. A tetanus antitoxin titre of 0.01 IU/ml is an international approved level of protection. However, literature cited a range of 0.01 to 0.15 IU/ml [5-9]. It can be measured by the widely used indirect enzyme linked immunosorbent assay (ELISA), however, it may give false-positive results. Furthermore, the level of 0.01 IU/ml as determined by an indirect ELISA may not be equivalent to the same level of antitoxin determined by the standard toxin neutralization method [7]. Some studies set an even higher titer of 1.0 IU/ml below which antibody levels are regarded as non protective [5-9].
Many factors affect the level of antitetanus antibodies in any given individual. For instance, higher levels are reported in males compared to females [7, 10], in the younger than older population [11, 12], and in vaccinated compared with non-vaccinated. A direct relationship exists between the degree and duration of tetanus immunity and the number of tetanus toxoid received [7]. Anti tetanus immunity tends to wane as more time passes since last vaccination [7, 13]. Primiparity, residence in a rural area and lack of antenatal care are documented risk factors for antitetanus seronegativity [6].
This study aimed at evaluating immunity against tetanus in women in Sudan in terms of seroprevalence of anti-tetanus antibodies and its association with factors such as age, gravidity, number of TT doses and time elapsed since last dose.
Materials and Methods
This cross-sectional study was carried out in the antenatal clinic of Omdurman Maternity Hospital, September 2011. Thirty-nine pregnant women consented to participate, were randomly included in this study. Regarding each participant, a pre-structured questionnaire was filled; a venous blood sample was collected in a plain tube. Then, all samples were transferred to the serology laboratory at Omdurman Military Hospital, where sera were separated, transferred to fresh plain tubes and kept at -20 C° until use.
Serum levels of antitetanus antibodies were measured using a commercially available ELISA kit (VaccZyme, Birmingham, United Kingdom). The manufacturer’s instructions were followed. The readings of the control sera were used to plot a curve from which the readings of the samples were deduced. Results were expressed in international units per milliliter (IU/ml). They were evaluated as following: <0.15 IU/ml was considered to be susceptible, 0.15 – 0.99 IU/ml as having basic protection, while 1.0 IU/ml or more was considered as full protection.
Data were analyzed by computer using SPSS version 16. The Chi-squared test was used to evaluate the differences between groups. A p value of < 0.05 was considered significant.
Results
Study population: Following informed consents, a total of 39 pregnant women were included in this study. They presented for antenatal care at Omdurman maternity hospital. Their ages ranged from 17 to 40 years (mean = 28.4 ± SD 5.78 years).
The concentration of serum anti-tetanus antibodies among the study group: It ranged from 0.02 to 9.94 IU/ml (mean = 4.39 ± 3.69 SD). The majority of the study group (69.2%) exhibited fully protective levels.
Anti-tetanus antibody concentration and vaccination status: The concentration of antitetanus antibodies was found to be significantly associated with the vaccination status (p value = 0.00). Women who received at least one dose of tetanus toxoid vaccine revealed variable levels of protection. On the other hand, all three women who had no history of vaccination were typically susceptible.
Antitetanus antibody concentration among different age groups: There was no significant difference in the antitetanus antibody concentration among different age groups (p value = 0.22). The rates of full protection among the age groups 20 - <30 and 30 – 40 years were 80% and 57.1% respectively.
Antitetanus antibody concentration and gravidity: The gravidity ranged from 1 to 8 among the study group with no significant difference in the concentration of anti-tetanus antibody (p value= 0.26). Generally, those who had 4 or less pregnancies had better protection, while those with a gravidity of 5 or more tended to have lower immunity against tetanus.
Antitetanus antibody concentration and the number of doses of tetanus toxoid: The antitetanus antibody concentration differed significantly with the number of tetanus toxoid doses (p value = 0.01). Those who had not received any vaccination were 100% susceptible, while receiving 2, 3 or 5 doses resulted in full protection in 78.6%, 80% and 71.4% respectively. Among those who received 5 doses, one was having basic protection, the other one was susceptible. But respectively, 6 years and 15 years has passed since their last dose.
Antitetanus antibody concentration and the time elapsed since last dose of TT: Antitetanus antibody concentration indeed differed with the time that has passed since the last vaccination (p value = 0.00). In particular, those who received their last dose within 5 years showed levels of full protection ranging from 40% to 95%. While after more than five years since the last dose of TT, only one out of seven was still fully protected. The highest level of protection was among those who received their last dose within 6 months.
Discussion
Various forms of tetanus toxoid stimulate the production of antitetanus antibodies [7, 14]. To assess the immunity against tetanus in a certain community, rates of vaccination coverage are better be supplemented by measuring the serum levels of antitetanus antibodies because the latter gives a better idea about the true levels of protection [5, 6]. Different in-vivo and in-vitro techniques can be applied for that purpose. The protective titre differs according to the technique used [7]. In neutralization test, 0.01 IU/ml is taken as the minimum protective level. But with immunoassay methods, titres can be as high as 0.15 IU/ml because of false positive results. An antibody concentration of 1.0 IU/ml is thought to secure life-long protection [5-9]. Indirect ELISA was used in this study because of its availability and relative simplicity compared to other methods. Accordingly, a concentration of 1.0 IU/ml or more was considered to provide full protection, while a concentration less than 0.15 was associated with susceptibility. Basic protection was defined as a concentration in the range of 0.15 – 0 .99 IU/ml.
In this study, the overall rate of immunity against tetanus was 84.6 %. However, the rate of fully protected women was 69.2 %, which correlates with reported figures from Egypt (68%) [15], United States (70% & 72 %) [5, 8], Germany (72%) [16] and Turkey (80%) [17]. All these studies employed indirect ELISA with a cut off value of 1.0 IU/ml.
Immunization during pregnancy leads to protective seroconversion [18]. In this study, there was a significant association (p value = 0.00) between vaccination status and the concentration of antitetanus antibodies. Those with a negative vaccination history were all susceptible, while receiving at least one dose of TT resulted in diffe

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Keywords: antitetanus, Immunity, Tetanus Toxoid, Pregnancy, Sudan

Conference: 15th International Congress of Immunology (ICI), Milan, Italy, 22 Aug - 27 Aug, 2013.

Presentation Type: Abstract

Topic: Adaptive Immunity

Citation: Elmahdi SA, Bakheit KH and Musa AM (2013). Seroprevalence of Anti-tetanus Antibodies in Women attending Omdurman Maternity Antenatal Clinic in Sudan. Front. Immunol. Conference Abstract: 15th International Congress of Immunology (ICI). doi: 10.3389/conf.fimmu.2013.02.00334

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Received: 24 Mar 2013; Published Online: 22 Aug 2013.

* Correspondence: Ms. Salma A Elmahdi, Faculty of Medicine Khartoum University, Department of Bichemistry, Khartoum, Khartoum, 1111, Sudan, salma_elmahdi@yahoo.com