Measurement of Tetanus Antitoxin in Oral Fluid a Tool to Conduct Serosurveys Milagritos D
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ORIGINAL STUDIES Measurement of Tetanus Antitoxin in Oral Fluid A Tool to Conduct Serosurveys Milagritos D. Tapia, MD,* Marcela F. Pasetti, PhD,* Lilian Cuberos,* Samba O. Sow, MD, MSc,† Mama N. Doumbia, MD,† Modibo Bagayogo, MD,† Karen L. Kotloff, MD,* and Myron M. Levine, MD, DTPH* urveys of the prevalence of tetanus antitoxin play an Background: Serosurveys that measure tetanus antitoxin can com- important role, particularly in developing countries, in plement immunization coverage surveys to allow evaluation of S objectively assessing the immune status of populations and immunization services in developing countries. Measurement of IgG tetanus antitoxin in oral fluid was investigated as a practical and the performance of immunization services. Because neonatal noninvasive alternative to and correlate of serum antibodies. and maternal tetanus control in developing countries is largely Methods: Serum and oral fluid were collected from Malian infants, based on immunization of pregnant women with tetanus toxoid, tetanus antitoxin serosurveys in women of childbearing age can toddlers and adults (males without a history of tetanus vaccination). 1 Specific IgG tetanus antitoxin was measured by enzyme-linked immu- identify high-risk, underserved populations. Measurement of nosorbent assay in serum (S-ELISA) and oral fluid (OF-ELISA). tetanus antitoxin also provides a helpful adjunct to immunization Results: One hundred forty-two pairs of serum and oral fluid coverage surveys in 12 to 23 month olds to assess how well samples were collected from infants, 35 pairs from toddlers and 35 services of the Expanded Program on Immunization (EPI) are pairs from adults. IgG tetanus antitoxin titers measured by OF- reaching infants. Measurement of tetanus antitoxin is especially useful because, with rare exceptions, this antibody is the result of ELISA were 100-fold lower than those measured by S-ELISA but 2 they correlated strongly (r ϭ 0.90, P Ͻ 0.001). All 35 toddlers who immunization and not natural disease or subclinical exposure. had received 2 or 3 doses of diphtheria–tetanus–pertussis (DTP) Until recently, collection of serum was required to con- vaccine (100%) had serum tetanus antitoxin levels Ն0.15 IU/mL duct population-based seroprevalence studies and to assess se- and 28 of 35 (80%) had oral fluid values Ն0.0015 IU/mL. Among rologic responses to pathogens or vaccines. This is problematic adults lacking a history of tetanus immunization, only 6 of 35 in developing countries where the prevalence of human immu- (17.1%) had serum titers Ն0.15 IU/mL and 4 of 35 (11%) had oral nodeficiency virus (HIV) or hepatitis C virus infection is high 3 fluid titers Ն0.0015 IU/mL in oral fluid. because handling blood constitutes a hazard for health workers. Conclusions : IgG tetanus antitoxin in oral fluid correlates well with In addition, cultural beliefs about blood drawing may hinder 4 5 levels in serum. OF-ELISA values Ն0.0015 IU/mL constitute pro- recruitment and participation, thereby biasing the sample. tection against tetanus and in subjects Ͼ12 months of age imply Since the early 1990s, investigators have analyzed oral multiple prior contacts with immunization services. IgG tetanus fluid as an alternative to serum. Oral fluid, a mixture of antitoxin measured by OF-ELISA provides a logistically practical IgA-rich saliva and IgG-rich crevicular fluid (a transudate of 6 alternative for performing seroprevalence surveys. serum expressed at the crevice between the teeth and gums), has been used in disease surveillance in the United King- Key Words: immunization, coverage survey, tetanus, oral fluid, dom7,8 and India9 as well as outbreak investigations10,11 and Mali, serosurvey epidemiologic12–14 studies. Results have documented high (Pediatr Infect Dis J 2006;25: 819–825) sensitivity and specificity. Several oral fluid assays are being developed as noninvasive alternatives to serum-based testing and licensed commercial kits are already available for detec- tion of human antibodies to HIV (OraSure Technologies, Inc., Bethlehem, PA)15 and measles (Microimmune, U.K.).16 Accepted for publication June 5, 2006. Oral fluid sampling may also be well suited to assess From the *Center for Vaccine Development, University of Maryland School of Medicine, Baltimore, Maryland; and the †Centre pour le De´veloppe- the performance of immunization services, including immu- ment des Vaccins, Mali, Bamako, Mali. nization coverage and cold chain integrity. In underserved Presented in part at the 8th Annual Conference on Vaccine Research, May areas of developing countries, it is difficult to assess objec- 9–11, 2005, Baltimore, MD. tively the performance of immunization programs because The work was supported by a grant from the Bill and Melinda Gates Foundation (M. M. Levine, Principal Investigator). surveillance systems for most infectious diseases are rudimen- Address for correspondence: Milagritos D. Tapia, MD, Center for Vaccine tary and confirmatory laboratory diagnostics are not available. Development, University of Maryland School of Medicine, 685 W. Estimates of immunization coverage that rely on vaccination Baltimore St., Rm. 480, Baltimore, MD 21201. E-mail mtapia@medicine. records or parental recall may provide inaccurate results, de- umaryland.edu. 17–20 Copyright © 2006 by Lippincott Williams & Wilkins pending on the study population. Furthermore, because the ISSN: 0891-3668/06/2509-0819 vaccine cold chain may be faulty, infants can be vaccinated DOI: 10.1097/01.inf.0000232629.72160.bb (ie, inoculated) but not successfully immunized as a result of The Pediatric Infectious Disease Journal • Volume 25, Number 9, September 2006 819 Tapia et al The Pediatric Infectious Disease Journal • Volume 25, Number 9, September 2006 vaccine damage caused by excessive fluctuations in temper- Samples of blood and oral fluid were obtained from all ature.21 Whereas collecting blood on a large sample of young participants at the time of inclusion. All 9- to 10-month-old children for this purpose would be a daunting logistical participants received measles vaccination according to the challenge in a developing country setting, oral fluid sampling Malian EPI recommendation and from these infants, a second offers a more practical approach. To explore this possibility, pair of samples was obtained 3 to 5 weeks later. Dates of we conducted 2 cross-sectional surveys of infants, toddlers vaccination of the infants and toddlers, as noted on the and adults living in Kangaba, Mali, and measured IgG tetanus vaccination card or the clinic log book, were recorded. antitoxin in paired serum and oral fluid specimens. Blood samples were centrifuged and the serum was aliquoted and stored in a dry shipper (Ϫ170°C) for transport to Bamako. Oral fluid was collected using 2 sponge swabs MATERIALS AND METHODS (Oracol; Malvern Medical Developments Limited, Worces- Study Site. Mali, a land-locked country in West Africa with an ter, U.K.), each consisting of a sponge attached to a plastic infant mortality rate of 122 per 1000 live births,22 is divided into stick. The first swab was inserted in one side of the mouth and 9 administrative regions that are further apportioned into 58 rubbed along the gums for approximately 30 seconds or until cercles. Kangaba cercle, located in the Koulikoro region 100 km saturated. The swab was then placed in its container and from the capital, Bamako, has a population 80,923 spread over stored on cold packs. The same procedure was repeated for 60 villages. Health care in Kangaba, including immunization, is the second swab on the opposite side of the mouth. Within 4 provided at 10 health centers. These studies were completed at 2 hours, the oral fluid was expressed from the sponges in the centers that provide care for Salamale´ and Kangaba villages. following manner: the sponges were removed from each of Primary healthcare workers who provide immunization the swabs and placed into a 10-mL syringe. The bottom of the services are expected to document immunizations on a card syringe was placed tip-down in a cryotube and both were (given to the parent) and in a clinic log book (in which all centrifuged in a tube shield for 20 minutes at 2500 rpm vaccines administered at a given facility are recorded). In (Medilite; Thermo IEC, Needham Heights, MA). The oral most instances, the vaccination card also lists the child’s date fluid collected was measured and an equal volume of preser- of birth or the age of first contact with health care personnel, vative (0.5% Tween 20, 0.01% chlorhexidine digluconate) usually for bacille Calmette-Gue´rin vaccination. Local health was added. Aliquots of serum and oral fluid samples were authorities currently calculate coverage for the 3-dose regi- stored and sent in a dry shipper to the Applied Immunology men of diphtheria–tetanus–pertussis (DTP3) by dividing the Laboratory at the Center for Vaccine Development in Balti- total number of doses of DTP3 vaccine administered by the more, MD, for analysis. number of children in the target population (children less than Serum Tetanus Antitoxin Enzyme-Linked Immunosorbent Assay. 1 year old). Official health statistics indicate that in 2003, Immulon II plates (Thermo Labsystem, Franklin, MA) were 69% of 12- to 23-month-old children in Mali had received coated for 3 hours at 37°C with tetanus toxoid (Staten Serum DTP3 vaccine.22 In 2002, DTP3 coverage was reported as Institute, Copenhagen, Denmark) at 5 g/mL in phosphate- 83% in Kangaba cercle. buffered saline (PBS), pH 7.4. Plates were blocked overnight Study Review and Informed Consent. The Ethics Committee at 4°C with 10% dried milk (Nestle USA, Inc., Glendale, CA) of the Malian Medical University (Faculte´deMe´decine, in PBS. After each incubation, plates were washed 6 times Pharmacologie et Odonto-Stomatologie- FMPOS) and the Uni- with PBS containing 0.05% Tween 20 (PBST). Samples were versity of Maryland Baltimore Institutional Review Board plated in 2-fold dilutions in 10% dried milk in PBST (PBSTM) approved the studies described here and community and individual consent were obtained as previously described.23 and then incubated for 1 hour at 37°C.