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Seroepidemiology of poliovirus antibody among the children in Eastern Turkey.

Background & objectives: Data on immunization are generally based on questionnaire methods or evaluation of health records in most of the developing countries like Turkey. Therefore, serological studies are useful to appraise the impact of vaccination programmes and to improve immunization policies. This serological study was undertaken to determine the immunity status of children to poliovirus in Eastern Turkey.

Methods: A cross-sectional and community-based field study was done with the sampling method of 30 clusters recommended for field studies. A total of 204 children aged 2-71 months were included. Complement fixation test was used to measure antibody titres to poliovirus serotypes. Subjects with serum antibody titres as 1:10 and lower were accepted as seronegative. A semi-structured questionnaire and official records of health care units were used to gather information about status of vaccination.

Results: Of the 204 children included, 54.4 per cent were boys and mean age was 31.5 [+ or -] 19.8 months; 26.5 per cent of the children were seronegative. According to official records 64.7 per cent of subjects were full vaccinated. Sensitivity and specificity of official health records were 83.6 and 67.3 per cent in relation to immunity status of children, respectively. Regarding number of OPV doses given to children, the sensitivity and specificity of parents recall in relation to official records were 98.0 and 17.4 per cent, respectively.

Interpretation & conclusions: Approximately, one of four children was determined to be seronegative. This high seronegativity brings risk to control of polio in Eastern Turkey which is at the post-elimination era since 1998. Additionally, parents recall did not provide reliable information to predict the immunity status and number of OPV doses given to children.

Key words Antibody--children--polio--seroepidemiology


Poliomyelitis is a highly infectious disease caused by a virus that mainly affects children under five years of age. There is no cure for polio; it can only be prevented (1,2). In 2003, only 677 cases of poliomyelitis had been reported in the world; representing a greater than 99 per cent reduction from 1998 (3,4). On June 21, 2002, the Regional Commission for the Certification of Poliomyelitis Eradication certified that the European Region was free from indigenous wild poliovirus transmission. The last known case in European Region of polio caused by indigenous wild poliovirus transmission occurred in Southeast Region of Turkey in November 1998 (5-8).

The Sabin oral polio vaccine has been used as a preventive measure along with the national immunization programme (NIP) in Turkey since 1985, and the recommended vaccination schedule requires administration of three doses of oral polio vaccine (OPV) at 2, 3 and 4 months of age as primary immunization. Reinforcement doses are given at 18 months and at the age of 7 yr. Additionally, between 1995-2004 national polio immunization days were added to current routine NIP (9).

In general, the data on immunization are based on questionnaire methods or evaluation of health records in Turkey. According to the data based on questionnaire methods, in 2004 three dose OPV vaccination rate for children aged 0-12 months was significantly lower (75%) in Eastern Turkey than that in Western Turkey (92%) (9). It has been difficult to obtain attainable health services in Eastern Turkey because Eastern Turkey is geographically disadvantaged and socio-economical status of population is relatively low. There was also lack of physicians with less number of operational primary health care units.

There are many shortcomings of questionnaire methods in indicating immunization status in a population, especially where health information system, health services, and education are not at the optimum level. Therefore, serological studies are useful to appraise the impact of vaccination programmes and to improve immunization policies (3-10).

We carried out this serological study to determine the immunity status of children to poliovirus in Eastern Turkey.

Material & Methods

Study design and subjects: This was a cross-sectional and community-based field study conducted in 2004. Subjects were the children aged between 2-71 months living in Erzurum province from Eastern Turkey. Erzurum is a province with approximately one million population where highly disadvantaged groups (low socio-economic level with inadequate access to health services) are living. The sampling method of 30 clusters recommended for field studies by the WHO was used (11). The subjects were selected from 32 clusters being stratified according to residential area (urban/rural). Each street in urban area and each village in rural area was assigned as one cluster, and 7 children were included from each cluster. Therefore, the total study population was 224 children. Children suffering from poliomyelitis and having a history of acute flaccid paralysis were excluded.

A semi-structured questionnaire, immunization cards of children and official records of health care units were used to gather information about vaccination status of children. The questionnaire was filled by researchers with face-to-face technique. With the questionnaire, vaccination history (parent recall) and sociodemographics were determined. Information was directly obtained from mother and/or father of the child.

If a subject was vaccinated with all required number of doses according to his/her age, he/she was accepted as "full vaccinated". If subjects had missing doses, they were classified as incomplete vaccinated. Children who were never vaccinated, were accepted as "unvaccinated". Number of OPV doses and status of vaccination were determined according to official records (12) and parent recall.

Blood samples and measurement : The serum was separated by centrifugation and frozen at -20 [degrees]C until the test was performed. A complement fixation test (Institute Virion Ltd, Switzerland) was performed to detect anti-polio antibodies against serotypes 1, 2 and 3. A positive antibody titre to poliovirus 1, 2, 3 complement fixation antigen indicated a contact with the virus or polio vaccine. Subjects with serum antibody titres of 1:10 and lower were accepted as seronegative.

Ethics and consent : The study protocol was approved by the Ethical Committee of Ataturk University and Ethics Panel of Regional Health Directorate of Erzurum Province. Written informed consents of parents were obtained. A paediatrician who accompanied the research team also examined the subjects who had any health problem.

Statistical analysis : Chi-square test was used to determine the association between sociodemographics, number of OPV doses and serum antibody titres. Sensitivity, specificity, positive and negative predictive values (PPV, NPV) of official records and parent recall was calculated. Statistical procedures were carried out using the Epi Info version 6.04 developed by Centers for Disease Control and Prevention, Atlanta, USA.


Of the study population (n=224), 8 children (3.6%) who could not be reached, 9 children whose parents (4.0%) did not accept to participate and three children (1.3%) whose blood samples could not be obtained, were excluded from the study. Therefore, the data in the study were obtained from 204 (91.1%) children.

Of these 54.4 per cent (n=111) were boys and mean age was 31.5 [+ or -] 19.8 months (median=29.9, range 2-71 months); 23.5 (n=48) and 19.1 per cent (n=39) of the children were at 24-35 and 2-11 months of age, respectively. Mothers of 44 (21.6%) children and fathers of 3.9 per cent (n=8) were illiterate. One hundred fifty three children (77%) were living in urban area; 73.5 per cent (n=150) of the families perceived their economical status as moderate. Level of mothers' and fathers' education did not differ according to residential area.

As the serum antibody levels of 1:10 and lower titre were considered as seronegative, 26.5 per cent (n=54) of the children were seronegative. The seronegativitiy did not differ according to gender; 27.9 and 24.7 per cent of the boys and girls were seronegative, respectively (Table I). Age was found to be a significant determinant for seronegativity. The highest seronegativity was seen in children between 12-23 months of age. The seronegativity in children at 2-11 and 60-71 months were significantly lower than other age groups (P<0.05). For children between 12-23 months of age (in which the children should receive the first reinforcement OPV dose in Turkey), the seronegativity in children who received three and less OPV doses was more than two fold higher compared to four and more doses (48.3 vs 19.7%).

Half of the children whose fathers were illiterate were seronegative. Of the children who were living in urban residential area, 30.0 per cent were seronegative and this rate was significantly higher than the children living in rural residence (P<0.05). Seronegativity was found to decrease with the increasing number of OPV doses (Table I). Seronegativity status according to number of OPV doses in children in Erzurum was shown in the Fig.

Validity of official records and parents recall in relation to child serological status was shown at Table II. According to official records 64.7 (132) and 26.5 per cent (54) were full vaccinated and unvaccinated, respectively. Whereas, parents declared that 80.4 (164) and 5.4 per cent (11) were full and unvaccinated, respectively. According to official records, 88.6 per cent of full vaccinated children were seropositive whereas it was 71.9 per cent according to parent recall. Sensitivity and specificity of official health records were 83.6 and 67.3 per cent in relation to immunity status of children, respectively. Unexpectedly, it was determined that parents recall was more sensitive but less specific than official records. Positive and negative predictive value of official records were higher than parents recall (Table II).


Validity of parents recall regarding number of doses in relation to official records was shown in Table III. The sensitivity and specificity of parents recall in relation to official records were 98.0 and 17.4 per cent, respectively.


With this cross-sectional seroepidemiological field study, we showed that considerable number of children were sero-negative. Although, there have been no polio cases due to wild poliovirus since 1998 in Turkey (13), the children are at the risk and vulnerable to polio because of high seronegativity. This low seroconversion rate might be due to various reasons. The major reason was low proportion of full vaccination in our study group. Other reasons might be concurrent enteroviral infections, interference among serotypes of OPV and poor hygiene (14,15). Additionally, poor maintenance in cold chain and suboptimal practices of vaccine handling could be attributed to low seropositivity (3). Night-angle had reported that control of poliomyelitis could be achieved by properly immunizing the 80-85 per cent of the population (16). Compared to that, full vaccination rate in children according to official records in our study was significantly lower. This indicates risk for poliomyelitis control in the region. In 2005, the proportion of full vaccination to polio in the study region has been over 75 per cent (17).

The overall seropositivity in our study was 73.5 per cent. This seropositivity was lower than the similar studies carried out in other countries (18-25). Seronegativity in children was higher in urban areas than rural. We considered that this unexpected result was possibly due to immigration to Erzurum city center from rural areas.

Unplanned habitation and high population growth rate may be the other reasons. In other words, immunization efforts in rural areas may be easier than in urban areas. Like our study, two other studies carded out in different developing countries did not determine significant differences according to residential area (26,27).

In this study, it was observed that illiteracy of fathers might be a risk factor for polio. On the other hand, similar risk was not found between education of the mother and immunity status. Men play dominant role in decision making in Eastern Turkish population. Cultural differences may play a role in forming of attitudes and behaviours towards vaccination.

There was a positive trend between antibody levels and the number of vaccine applications. Each application provided approximately 1.2-fold increase in the percentage of immunity level, and it was an anticipated finding in the present study. The percentage of seronegativity among the unvaccinated children was approximately two-fold higher than children who received four doses of vaccine. Chen et al (28) determined that the predictor of seropositivity to poliovirus was the number of doses of received oral poliovirus vaccine. In our study, the seronegativity in children aged 12-23 months who received [less than or equal to] 3 OPV doses was more than twofold higher compared to children with [greater than or equal to] 4 OPV doses. The application of reinforcement doses of polio is essential to achieve higher seropositivity in children.

According to official records, seronegativity in unvaccinated subjects was more than 3-fold higher compared to parents recall. Also, seropositivity in full vaccinated children was higher for official records than parents recall. Incompatible with these findings, positive and negative predictive values for official records were higher than parents recall. These findings indicated that reliable estimation about the immunity status of children could not be obtained by parental declaration. Therefore, physicians should not trust vaccination history obtained from parents where health records and immunization efforts were not sufficient. In contrast to our study, in three other studies conducted in Mexico, United States and South Africa, parental declaration towards polio vaccination history was found to be reliable (26,28,29).

In our study, sensitivity of parents recall was higher than official records. This could be due to low number of subjects who were declared to be unvaccinated. Other than sensitivity, specificity and negative predictive value of parents recall were low. These findings indicated that parents recall was unreliable to predict immunity status of children.

In conclusion, our data showed that a large number of children were seronegative for poliovirus antibody. As Turkey is at the post-elimination era for poliomyelitis, it is important to reach high immunization proportions to sustain current situation in Eastern Turkey. In addition, parents recall did not provide reliable information to predict the immunity status and number of OPV doses given to children. Therefore, seroprevalance studies should be performed to obtain reliable information about the immunity status of children for polio in disadvantaged regions of developing countries.


Authors thank the Regional Health Directorate of Erzurum and acknowledge The Research Fund of Ataturk University for financial support.

Received March 6, 2006


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Reprint requests: Dr Serhat Vancelik, Assistant Professor, Ataturk Universitesi Tip Fakultesi, Halk Sagligi Anabilim Dali 25240 Erzurum, Turkey


Serhat Vancelik, Asuman Guraksin, Ahmet Ayyildiz * & N. E. Beyhun

Departments of Public Health & * Microbiology in Ataturk University, School of Medicine Erzurum-Turkey
Table I. Serum antibody titres according to sociodemographics
and number of OPV doses

 Serum antibody titres

 ([less than 1:10 1:20 1:40 1:80
 or equal to]
Sociodemographics 1:10) n=54) n=46 n=52 n=43 n=9

Boys 27.9 25.2 24.3 18.9 3.6
Girls 24.7 19.4 26.9 23.7 5.4
Age (months) *:
2 - 11 10.3 23.1 25.6 35.9 5.1
12 - 23 41.0 20.5 17.9 15.4 5.1
24 - 35 31.3 35.4 16.7 14.6 2.1
36 - 47 40.0 20.0 24.0 4.0 12.0
48 - 59 21.9 18.8 31.3 25.0 3.1
60 - 71 9.5 4.8 52.4 33.3 0.0
Fathers' education *:
Illiterate 50.0 12.5 12.5 25.0 0.0
Primary school 32.5 22.9 25.3 16.9 2.4
High school or upper 24.0 23.0 26.5 23.9 6.2
Mothers' education
Illiterate 27.3 27.3 20.5 20.5 4.5
Primary school 25.2 22.2 27.4 27.0 4.4
High school or upper 32.0 16.0 24.0 24.0 4.0
Residential area *:
Urban 30.2 22.6 20.8 21.4 5.0
Rural 13.3 22.2 42.2 20.0 2.2
Number of OPV doses:
0 34.7 20.0 30.7 10.7 10.7
1 27.3 9.1 9.1 45.5 45.5
2 25.0 25.0 25.0 25.0 25.0
3 22.9 31.3 14.6 27.1 27.1
4 19.0 20.7 31.0 24.1 24.1
Total 26.5 22.5 25.5 21.1 4.4

* P<0.05

Table II. Validity of official records and parent recall
in relation to child serological status


 Seropositive Seronegative
 (>1:10) ([less than
 or equal to]

 n % N %

records (n=186) *:
Full vaccinated 117 88.6 15 11.4
Unvaccinated 23 42.5 31 57.5

recall * (n=175):
Full vaccinated 118 71.9 46 28.1
Unvaccinated 9 81.8 2 18.2

 Sensitivity Specificity PPV NPV

Official records 83.6 67.3 88.6 57.5
Parent recall 92.9 4.2 71.9 18.2

PPV, positive predictive value; NPV negative predictive value

* Subjects whose parents declared them as incompletely
vaccinated were excluded

Table III. Validity of parents recall regarding number
of doses in relation to official records

 Official records

Parent >4 dos 1-3 doses
recall n n

>4 doses 48 (98.0) 57 (82.6)
1-3 doses 1 (2.0) 12 (17.4)
Total 49 (100.0) 69 (100.0)

Sensitivity = 98.0, Specificity = 17.4, PPV = 45.7, NPV = 92.3,
Figures in parentheses are percentages NPV, negative
predictive value; PPV, positive predictive value
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Author:Vancelik, Serhat; Guraksin, Asuman; Ayyildiz, Ahmet; Beyhun, N.E.
Publication:Indian Journal of Medical Research
Article Type:Clinical report
Geographic Code:7TURK
Date:Dec 1, 2007
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