Seroprevalence of Specific Antibodies to Treponema pallidum in Blood Donors

Results: The seroprevalence of specific antibodies to T. pallidum among blood donors was found 0.42% (95% CI= 0.3-0.5%). There was an increasing trends of syphilis as the age of the donors increased (Cochrane-armitage test, P < 0.001). The seroprevalence in males was 0.45% and in females was 0.24% (P >0.05), in first time donors was 0.36% and in repeated donors was 0.48% (P > 0.05), among volunteer donors was 0.41% and among replacement donors was 0.50% (P > 0.05).


INTRODUCTION
In Nepal, prevalence of sexually transmitted infections (STIs) is quite high and estimated to be around 3% of the population. 1 The major hospitals of the country report higher prevalence of gonorrhea followed by syphilis, chancroid and herpes genetalis. 2eponema pallidum is a chronic infection with many diverse clinical manifestations that occur in distinct stages. 3Syphilis can be transmitted by sexual contact, transplacental transfer and less commonly through indirect routes (contaminated objects, tattoos) and blood transfusions. 4,5The treponemal tests have good sensitivity at all stages of disease and indicate either present or past evidence of Syphilis 6 .
The risk of transmission through blood is negligible due to improved donor selection, uniform serologic testing of all blood donors and increased trend of transfusion of refrigerated blood components. 7Transmission via blood products is nonetheless theoretically possible since organisms may survive for upto 5 days in blood stored at 4 o C. 3,8 In Nepal, the scenario of post transfusion infection is unclear however according to National Center for AIDS and STD Control (NCASC), 24 of total reported HIV positive cases are described to be associated with blood transfusion or organ transplantation. 9e world health organization (WHO) estimates that 12 million new cases of syphilis occur each year and the greatest number of cases was estimated to have occurred in South and Southeast Asia. 10 In context of Nepal, various studies among high risk individuals have reported that the seroprevalence of Syphilis ranges from 2.5-24.7%. 11,12The seropositivity of syphilis among blood donors in Bhairahava, western Nepal, has been reported to be 0.39% on the basis of positive RPR test 13 .So far we know, the seroprevalence study of Syphilis using specific treponemal tests among a representative sample of Nepalese blood donors has not been published.This study is expected to be useful in making plans and policies for management of safe blood supply in Nepal and would generate the data regarding seroepidemiology of Syphilis in healthy looking general population.

METHODS
This was a descriptive cross sectional study conducted in Central Blood Transfusion Service (CBTS), Nepal Red Cross Society (NRCS), Exhibition Road, Kathmandu, from December 1, 2006 to August 1, 2006.Blood donors, donating blood in CBTS or in Mobile camps organized in Kathmandu valley were selected as study population.All blood donors selected for donation as fulfilling per criteria of CBTS were included in the study except those who already donated previously within the specified time period of this study.A total of 24,000 blood donors were included in the present study.Blood donors were tested for detection of specific antibodies against Treponemal pallidum by enzyme linked immunosorbent assay (ELISA) (Enzygnost Syphilis, Dade Behring, Marbug, Germany) in an automated ELISA processor (Behring ELISA processor III, Marbug, Germany).An initial reactive test result was reconfirmed by repeat testing and repeatedly reactive samples were considered seropositive.The data was entered in Microsoft excel spreadsheet collecting the information from Blood donor's form and was analyzed by the statistical software "SPSS ver 11.5".Chi -square test was used for test of association.
Before collecting the blood sample each donor was requested to fill the blood donors form and he/she was assured that the confidentiality would be strictly maintained during testing and recording for mandatory screening of blood for Transfusion transmitted infections as per guidelines of NRCS, CBTS.

RESULTS
The overall seroprevalence of specific antibodies against Treponema pallidum in Nepalese blood donors was 0.42 % (95% CI= 0.3-0.5%).There was significantly increasing trends in overall seroprevalence as the age increased and the result was consistent for both male and female donors (P <0.001) (Table 1, Figure 1).The mean age of the seropositive donors was 36.56 year (Std.dev=9.283).The seroprevalence was 0.45% among male donors and 0.24% among female donors but the difference was not statistically significant (P >0.05).The seroprevalence was higher among repeat donors than among first time donors, but the difference was not statistically significant (P >0.05).Among the 59 seropositive repeat donors, 34 (57.6%)donated 5 or more times.The seroprevalence was slightly higher among replacement donors than among volunteer donors and the difference was not statistically significant (P >0.05).

DISCUSSION
This study was conducted to reveal the seroepidemiology of specific antibodies to T. pallidum among Nepalese blood donors.Though the blood donation programs were organized in Kathmandu Valley, donors were from all over the country representing different caste and ethnicity.
Present study revealed that the seroprevalence of specific antibodies to T. pallidum among Nepalese blood donors was 0.42%.A similar seroprevalence was reported from Bhairahava, western Nepal, among blood donors, though nontreponemal test was used for screening in that study. 13The seroprevalence observed in present study was much less than in the study reported by Gupta et al.  2001) from Georgia.14- 17 .The seroprevalence observed in present study was slightly higher than the seroprevalence reported by Moiz et al.  (2004) from Pakistan and Gunduz et al. 18 (2005) from Turkey, the lower seroprevalence rate in these study was possibly due to the screening by non treponemal tests, as nontreponemal tests lack sensitivity at later stage of the disease and become negative in successfully treated patients. 19,20Using the specific treponemal screening test Garcia Montalvo has reported a slightly lower seropositivity among Mexican blood donors than in our present study. 21e study revealed considerably higher seroprevalence of syphilis among the male donors, though the difference was not statistically significant.The seroprevalence rate observed for male donors in present study was lower than in the study reported by Joshi et al. in a similar population but in that study RPR was used for screening. 22e study showed that there was increasing trends in seroprevalence of syphilis as the age of the donors increased and the result was consistent with both  significant, considerably higher seroprevalence rate among repeat blood donors revealed by present study was notable.This was possibly due to the lack of CBTS initiated donor notification and counseling of the TTIs seropositive donors as well as might be due to the ineffectiveness of donor education and counseling.
male and female donors, a characteristic of sexually transmitted infections.
Regular repeated donors are considered the safer blood donor groups and such type of donation has been encouraged worldwide.Though statistically non (2004) from India, Rahman et al. (2002) from Lahore, Pakistan, Matee et al. (2006) from Tanzania, and Butsashvili et al. (

Figure 1 .
Figure 1.Seroprevalence of specific treponemal antibodies in male and female blood donors according to different age groups.

Table 1 .
Seroprevalence of blood donors according to sex, age, times of donation and type of donation.
P for trends in male donors <0.001 and P for trends in female donors <0.001 (Cochrane-armitage test for trends).