Indian Journal of Medical Microbiology Medknow Publications on behalf of Indian Association of Medical Microbiology ISSN: 0255-0857 EISSN: 1998-3646 Vol. 29, Num. 1, 2011, pp. 72-73

Indian Journal of Medical Microbiology, Vol. 29, No. 1, January-March, 2011, pp. 72-73

Correspondence

Testing Hepatitis A virus antibody in oral fluid among the prospective vaccinees foster the need of new oral HAV rapid test

M Ahmed¹, SU Munshi¹, S Andalib², S Tabassum¹, MN Islam¹

¹ Department of Virology , Bangabandhu Sheikh Mujib Medical University, Dhaka-1000, Bangladesh
² Department of Microbiology , Medical College for Women's and Hospital, Uttara, Dhaka-1230, Bangladesh

Correspondence Address: S U Munshi, Department of Virology , Bangabandhu Sheikh Mujib Medical University, Dhaka-1000, Bangladesh, saifmunshi@yahoo.com

Date of Submission: 05-Dec-2009
Date of Acceptance: 01-Oct-2010

Code Number: mb11019

PMID: 21304203

DOI: 10.4103/0255-0857.76532

Dear Editor,

We reported earlier the higher prevalence of HAV infection among Bangladeshis. ^[1] As majority of the adults are naturally immune to HAV before they attain their 25 years of age, we had suggested pre-immunisation test for antibody against HAV (anti-HAV) in our vaccination strategy. But in reality, we found prospective young adults and children, including their parents, not keen to undergo the test, especially due to stress or pain caused by venipuncture and the additional cost of the vaccine. Oba et al. proposed that saliva would be an alternative for screening probable candidate of the vaccination against HAV. ^[2] In this context, we examined the probability of using commercially available HAV serum enzyme-linked immunosorbent assay (ELISA) kit (ETI-AB-HAVK-3, DiaSorin, Sallugia, Italy) with a few modifications ^[3] to detect total anti-HAV in oral fluid and compared with the results of serum ELISA test. We collected paired serum and oral fluid from 64 prospective vaccinees and found a good correlation (correlation coefficient, R² = 0.677) between the optical density (OD) values of the paired samples [Figure - 1]. Considering the serum ELISA result as a gold standard, we were able to identify correctly 39 persons as naturally immune and 18 persons as susceptible individuals from their saliva, while five study subjects were identified as false positive and two persons as false negative in the test. All the test validation indicators showed that salivary HAV antibody test has the potential of substituting HAV serum antibody test in identifying prospective HAV vaccinees [Table - 1]. The diagnostic accuracy of the test was 89.06% (95%CI: 79.1-94.6). We found slightly lower sensitivity and specificity of the saliva test in comparison to other studies. ^[2],[3] This discrepancy may be due to avoiding use of any special device for collection of saliva used by those investigators. But we think avoiding such device in return makes saliva collection even simpler and less expensive. The diagnostic odds ratio, which is a prevalence independent single indicator, shows that the odds for positivity among subjects with real HAV infection is 70 times higher than the odds for positivity among subjects without infection. The likelihood ratio of a positive test, i.e., the possible ratio of getting a positive test result among HAV positive subjects to the same result in HAV antibody negative individuals is very high (8.864). The likelihood ratio of a negative test, i.e., the ratio of a negative test result among HAV positive subjects to the same result in HAV antibody negative individuals is very low (0.126). The predictive value of a screening test is dependent on the prevalence of the disease among the population to be tested, as well as on the sensitivity and specificity of the test. ^[4] Therefore, taking into account the prevalence rate of HAV infection in Bangladesh which we reported before, ^[1] the saliva test shows high positive and negative predictive value (PPV, NPV) in our general population and among different age groups. Among age groups, i.e., 1-2, 3-5, 6-10, 11-15, 16-20 and >20 years, the PPVs were 61, 87.62, 96.41, 97.32, 99.83, and 100%, and NPVs were 97.82, 90.84, 72.32, 65.89, 10.77, and 0.08%, respectively. If an individual from the general population gets a positive result, there is 96.34% chance that the individual had suffered or is currently suffering from HAV, leaving only a 3.66% chance that it is a false positive result. On the other hand, for a negative result, there is 72.75% chance that the person had never suffered or currently is not suffering from HAV infection, leaving a 27.25% chance that it is a false negative result. This type of probability also holds true in any specific age group of Bangladeshis.

In the current study, samples were collected from all the prospective vaccinees on their first visit. The majority of them came to know on their second visit that they had immunity and they need not to get vaccinated against HAV. So we assume it would be better if we could offer a rapid oral total HAV antibody test on the first visit of a prospective vaccinee, which might avoid the inconvenience of second visit. Moreover, we hope it will be useful and encouraging for the children or an adult person to take the test before vaccination and would help in avoiding unnecessary immunological assault.

At present, there is only one rapid oral test used for routine and urgent diagnosis of HIV, and recently, another one is evaluated for HCV diagnosis. ^[5] We believe that in the existing situation, there is also a need for cheap oral rapid test of HAV antibody that might cut down a huge cost of immunisation in highly endemic countries and make vaccination against HAV more effective and successful.

References

1.	Ahmed M, Munshi SU, Nessa A, Ullah MS, Tabassum S, Islam MN. High prevalence of Hepatitis A virus antibody among Bangladeshi children and young adults warrants pre-immunization screening of antibody in HAV vaccination strategy. Indian J Med Microbiol 2009;27:48-50.   Back to cited text no. 1  [PUBMED]
2.	Oba IT, Miranda AM, Saraceni CP, Lemos MF, Senhoras RCFA, Moreira RC et al. Detection of hepatitis A antibody by ELISA using saliva as clinical samples. Rev Inst Med Trop S Paulo 2000;42:197-200.  Back to cited text no. 2
3.	Thieme T, Yoshihara P, Piacentini S, Beller M. Clinical evaluation of oral fluid samples for diagnosis of viral hepatitis. J Clin Microbiol 1992;30:1076-9.  Back to cited text no. 3  [PUBMED]  [FULLTEXT]
4.	Mausner JS, Kramer S. Screening in the detection of disease. In: Mausner JS and Bahn A K, editors. Epidemiology - An Introductory Text. 2 nd ed. Philadelphia: Saunders; 1985. p. 220  Back to cited text no. 4
5.	Walter Reed Evaluation OraQuick (R) HCV. (The Medical News Today website). Available from: http://www.medicalnewstoday.com/articles/120222.php. [last accessed on 2009 Oct 28].  Back to cited text no. 5

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