J Clh i@&mid id. 43, No. 12, pp. 1361-1367.1990 0895-4356/90 s3.00 + 0.00 Print& in Great Britain. All rights rcacrved Copyright Q 1990 Pergamon Rwa pk LOW GASTRIC ACID AS A RISK FACTOR FOR CHOLERA TRANSMISSION: APPLICATI0N OF A NEW NON-INVASIVE GASTltIC ACID FIELD TEST F. P. L. VAN L~oN,‘*~ J, D. CLEMENS,‘~ M. S’MAHRIBR, ’ D. A. SACK,‘.~ C. B. STEPHENSEN,~ M. R. KHAN,’ G. H. -lUNI,’ M. R. -o’~ and A. K. BANIK’ ‘International Centre for Diarrhoeal Disease Research, wgka lKi0, Bangladesh,2Center for Vatine Development, Baltimore, ‘Johna Hopkins University, Baltimore, Maryland and ‘University of Alabama, Birmingham,Alabama, U.S.A. (Received in revised farm 22 May 1990) Abstract-Although gast+ acid is thought to be an important host defense against axtain enteric infections, field studies of the role of gastric acid in preventing enteric infections have been hampered by the lack of a suitable non-invasive test. Because low gastric acid output (GAO) is an estabhshed risk factor for cholera, we assessed after validation, whether a new non-invasive test which estimates GA0 by measuring breath hydrogen excess after ingestioxrof magnesium and a stimulant of gastric acid secretion, could discriminate between persons at high and at low risk of developing cholera. Fifteen age-matched pairs, participants in the field trial of two oral cholera vaccines in rural Bangladesh, were tested. In each pair the “case” yas a person who had recovered from severe cholera at least 6 months before testing aird the “ control”wasa personwho resided in the home of a cholera patient hut remaiïred &i&cted. The stimulated breath hydrogen was higher in controls (median hydrogeh excess = 369 /.~no1/80 min) than in cases (median hydrogen excess = lSOpmo1/80min) (p -< 0.05) and was hlgher in controls in 12 out of 15 pairs. The results, whioh are consistent with past invasive assessments of the association between hypochlorhydria and cholera, suggest that this non-invasive test may be useful in evaluating GA0 in epidemiological field studies. Gastric acid Cholera Breath tests Caseins Cholera vaccine Oral INTRODUCMON Low gastric acid output (GAO) is associated with an increased risk of cholera and enterotox- igenic Escherichiu coli diarrhea [ 1-6]. In spite of its importante as a risk factor for these infee- tions, field studies of GA0 have been hampered by the lack of a suitable non-invasive test. Recently an oral magnesium breatb hydrogen test (OMBHT), which does not require gast& intubation, has been developed and valiited in clinical settings [7-9]. When magnesium is given orally, itreacts with gastric hydrochloric acid to liberate hydrogen, according to the following formula: Mg + 2 HCl*Mg*+ + 2 Cl- + H,. The hydsogen is then eructated or absorbed across the gut mucosa and, via circulation and lungs, exhaled. In the absente of gastric acid, there is no detectable increase in breath hydro- gen. The OMBI-IT, gives results comparable to 1361