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A new urea broth-based test to detect Helicobacter pylori presence in upper gastrointestinal biopsies
ELSEVIER
BACTERIOLOGY
A New Urea Broth-Based Test to Detect Helicobacter pylori Presence in Upper Gastrointestinal Biopsies Karl Weiss, Louise Poirier, Michel LaverdiPre, and Slobodan Ducic
The aim of this study was to evaluate the performmce of a simple and inexpensive komemade urea test (U-test) to defect Helicobacter pylori in upper digestive tract biopsies. We tested and compared the U-test with fkree other diagnostic methods: the C/o-test, and culture and pafkology in 110 patients randomly chosen at the endoscopy clinic. Wken using culture and/or pathology as the “gold standard,” H. pylori ZLVZS foundto exist in 54 patients. Pathology zoas positive in
50 cases (92.5%), culture iri 49 (90.7%), fke U-test in 45 (83.3%), and the C/o-test in 43 (79.6%). With regard to culture pathology, the sensitivities of the U-test and the Clo-test zoere 83.3% and 79.5%, respectively. Specificity was 200% for both methods. The K coefficient calculation between fke U-test and the Clo-test was 0.98. Tke results skozv that tke U-test is a reliable, fast, and inexpensive method for defecting H. pylori in upper gastrointestinal biopsies.
INTRODUCTION
Others such as serology are useful for epidemiologic studies but are not suitable for rapid diagnosis and for monitoring patient’s response after treatment (Barthel et al., 1990; Brown et al., 1993). Helicobacter pylori is known to produce one of the strongest bacterial ureases. This enzyme has the ability to split urea into ammonia and bicarbonates, thus creating an alkaline medium. The Clo-test (Delta West, Bentley, Australia) is a rapid, accurate, and easy to use detection method based on this enzymatic property (Brown et al., 1993; Cutler et al., 1995). Nevertheless, its cost is quite expensive in Canada, which prohibits extensive use of this diagnostic test. By using the same chemical principle, we designed a homemade urea broth test (U-test) for detecting the presence of H. pylori in upper gastrointestinal biopsies. The aims of this study were, first, to develop a rapid, easy to use, and inexpensive test (U-test) for H. pylori detection in upper gastrointestinal biopsies; and second, to compare this test with the Clo-test, as well as with two other detection methods used as the “gold standard” (culture and pathology).
Since 1983, peptic ulcer disease and gastritis have been strongly associated with the presence of Helicobatter pylori in the upper digestive tract (Blaser, 1992; Marshall et al., 1983; Murray, 1993). Several laboratory methods are used nowadays to detect the bacteria presence. Some investigative techniques such as the breath test, although noninvasive and sensitive, are cumbersome, use radioactive material, and require specialized equipment (Brown et al., 1993).
From the Department of Medical Microbiology and Infectious Diseases, HBpital Maisonneuve-Rosemont (K.W., L.P., M.L.), and the Department of preventive Medicine (S.D.), UniversitC de MontrPal, Montreal, Quebec, Canada. Address tqwint requests to Dr. K. Weiss, Department of Medical Microbiology and Infectious Diseases, HBpital MaisonneuveRosemont, 5415 l’Assomption, Montreal, Quebec Canada HIT 2M4. This study was presented in part at the 19th International Congress of Chemotherapy, 1995, Montreal, Canada (abstr no. 1106). Received 2.6 September 1995; revised and accepted 20 December 1995.
DIAGN MICROBIOL INFECT DIS 1996;24:61-64 0 1996 Elsevier Science Inc. 655 Avenue of the Americas, New York, NY 10010
0732.8893/96/$15.00 SSDI 0732-8893(95)00274-X
62
K. Weiss et al.
MATERIALS Population
AND METHODS
son, Cockeysville, MD, USA) and a Skirrow agar, which were incubated at 37°C for 7 days in a microaerophilic environment (85% N2, 10% CO,, 5% O,), obtained by adding a gas-generating pack (Camp$obacfer microaerophilic system; Difco) in a 2.5~liter sealed jar. Quality control of the microaerophilic atmosphere was assessed using a collection H. pylovi strain obtained from the Quebec provincial laboratory, plated on Brucella blood agar. Helicobacfer pylovi identification was achieved by performing a Gram stain and catalase and cytochrome oxidase reactions on isolated colonies. Furthermore, urease activity was detected by inoculating Christensen’s urea agar.
Studied
A total of 110 adult patients, referred to our endoscopy clinic for various gastrointestinal symptoms from February 1994 to March 1995, were randomly chosen and prospectively included in the study. Clinical preendoscopic diagnosis included gastritis, peptic ulcer disease, and nonulcer dyspepsia. For each patient, four 3-mm antral biopsies were taken close together, and the presence of H. pyIovi was systematically detected by four different methods: pathology, culture, Clo-test, and U-test.
Diagnostic
Pathology Warthin-Starry and Giemsa stainings were systematically done on each biopsy by the pathology department. Moreover, an immunoperoxidase-based detection method (Dako, Glostrup, Denmark) was added to the routine workup for the purpose of this study.
Tests
U-Test Our homemade test was prepared by adding 5 g of urea (Difco, Detroit, MI, USA) to 50 ml of distilled water. The pH was subsequently adjusted to 6.8, and 0.5 ml of the solution was added into individual plastic vials. One drop of a 6% phenol red solution (Difco phenol red broth base: 0.9 g in 15 ml of distilled water) was then added to the vials as a pH indicator. Once prepared, each batch was kept refrigerated in the endoscopy clinic at 4°C. On average, vials were used within 2 months after preparation. Before being used, the test material was warmed to room temperature. Biopsy specimens were put directly into the vials and left at room temperature. A positive reaction was defined as a color change of the medium within 2 h, from pale beige to purple-pink. For every batch, quality control was assessed by randomly inoculating a vial with a loopful of an H. pylovi strain obtained from the Quebec Provincial laboratory. Thereafter, every week a quality control test was performed on a randomly selected refrigerated vial.
Clo-Test This test was used according to the manufacturer’s instructions. A positive reaction was defined by a color change of the medium within 2 h inoculation with the biopsy. By definition, a biopsy sample was considered to be positive when the presence of bacteria was detected by either culture or pathology.
Statistical Analysis Comparison between tests was done using the difference between population proportions (Daniel, 1991). P values < .05 were considered to be significant.
RESULTS
Culture Biopsy specimens, rapidly transported to the microbiology laboratory in physiologic sterile saline, were immediately minced and homogenized. They were then plated on a Brucella blood agar (Becton DickinTABLE
1
Detection of Helicobacfer Different Methods”
Diagnostic test U-test Clo-test Culture Pathology No. of patients
A total of 54 patients out of 110 had a positive upper gastrointestinal biopsy by culture and/or pathology (Table 1). For 5 patients, biopsies were positive for H. pylovi by pathology but negative on culture. Of these,
pylovi in 110 Patients by Four
Total Positive
Test Results + + + + 38
+ + + 1
“+: positive upper gastrointestinal
+ f + 4
+ _ + + 2
_ _ + + 5
_ _ + _ 3
_ _ _ + 1
_ _ _ _ 56
biopsy; -: negative upper gastrointestinal
45/54 (83.3%) 43/54 (79.6%) 49/54 (90.7%) 50/54 (92.5%) 54 biopsy.
63
Urea Test for 11. pylori
four were also positive by the two rapid methods (Clo-test and U-test). In one patient, the bacteria was detected by pathology only. There was a perfect agreement between the different histology staining techniques, and Giemsa was as good as WarthinStarry, an observation already noticed by others (Gray et al., 1986). In three patients, culture was the sole positive test; however, growth was very light, probably reflecting a small inoculum below the detection threshold of the other diagnostic methods. Overall, biopsies were positive by pathology for 50 patients and by culture for 49; in nine cases there was disagreement between the two methods. When analyzing the results obtained with the rapid detection methods, results were very comparable between the Clo-test and the U-test. Although not statistically signi~cant, the latter was even able to detect two positive biopsies, confirmed by pathology and culture, which were not detected by the former. The reverse situation did not happen. The K coefficient (Jenicek, 1995) is a useful tool for measuring the external validity of a diagnostic test. It ranges from -1 (disagreement) through 0 (random agreement), to 1 (complete agreement). In our case, when comparing the Clo-test with our U-test, we found an almost perfect match between the two methods (K = .98). All positive U-test biopsies (45) were positive by either pathology or culture, with most of them (40) positive by both methods. Among the five negative biopsies by either pathology or culture, two of the four negative cultures occurred as a cluster; this suggests a possible technical problem with the specimen processing. No sample was positive by our U-test but negative by one of the two “gold standard” diagnostic tests. When compared with culture and/or histology used as a “gold standard,” sensitivities of both tests were 79.6% and 83.3%, respectively (Tables 2 and 3). A specificity of 100% was also recorded for both tests with regard to culture and/or histology. No method was perfect in detecting all positive samples. Statistically, there was no significant difference in terms of sensitivity among pathology, culture, and the U-test. TABLE
2
Comparison of the CLO-TestTM with Culture and Histology Culture/Histology
CLO-test
+ -
+
-
43 11 54
56
67
56
110
Total Sensitivity: 79.5% CI,, (72~87.1%) Specificity: 100% CI,, (9&l-100%) CI,,: 95% confidence
interval.
0
43
TABLE
3
Comparison of the U-Test with Culture and Histology Culture/Histology + + -
U-test Total
-
45
0
9
56
65
54
56
110
45
CI,, (76.3-90.1%)
Sensitivity:
83.3%
Specificity:
100% CI,,
(98.1-100%)
CI,,: 95% confidence interval.
The only significant difference was noted between pathology and the Clo-test (P = .026).
DISCUSSION HeEicobncter pylori is an increasingly important microorganism associated with many upper gastrointestinal pathologies, including certain types of gastric cancer (Blaser, 1992; Parsonnet et al., 1994). However, many questions still have to be elucidated regarding its detection as well as treatment (Peura, 1995). Basically two types of detection methods are available: invasive methods, necessitating an endoscopy, and noninvasive methods such as the breath test. Each category of tests has its drawbacks and advantages in terms of cost, rapidity, required equipment, and potential complications for the patients (Brown et al., 1993; Chodos et al., 1988). Although requiring an endoscopy, rapid urease tests have been singled out as the most cost-effective method to detect H. pylori (Peura, 1995). The major problems associated with this technique are the cost and the potential complications of an endoscopy. However, the test itself is the least expensive detection means and gives a rapid answer for treatment purposes. We developed our own test, bearing in mind the need for a rapid method comparable in efficacy to the Clo-test. The K coefficient calculation enables us to compare the performance and the reproducibility of our test with the Clo-test. The agreement between the two rapid detection methods was almost perfect (.98), suggesting that the U-test is very comparable to the former. One difference with the Clo-test resides in the absence of any bacteriostatic agent in our test. This does not seem to affect the test performance, which is why the 2 h cutoff point was chosen. Other urea-splitting bacteria present in the digestive tract such as Proteus species were unable to give a false-positive result in that time frame. If a 24-h reading time had been chosen, sensitivities of both tests would have increased. The Clo-test positive predictive value ranges between 90% and 98%
64
K. Weiss et al.
when read at 24 h (Barthel et al., 1990). Indeed, for the study purposes, a few specimens considered negative by the two m-ease tests became positive when read at 24 h. Nevertheless, by doing this, we lost a great advantage of these rapid tests, and the possibility of having false-positive results due to other bacteria arose. With a sensitivity reaching our homemade urea 83.3% (CI,,: 76.3%-90.1%)‘ broth test is a reliable method to detect H. ~~~~~~in upper gastrointestinal biopsies. It is very comparable to what has been previously found for the Clo-test by different groups (Cutler et al., 1995; Morris et al., 1989). Other rapid urease tests with satisfactory results have been reported. In their study, Westblom et al. (1988) used a l-h cutoff point and obtained a sensitivity of 67%. Although the concept of “gold stan-
dard’ tests is debatable (Peura, 1995), culture and histology with 100% specificity are the best candidates for this description (Barthel et al., 19901, which is why we decided to choose them as points of comparison. Our U-test could be useful in an outpatientoriented setting. Treatment directed against H. p$ori can be rapidly initiated in cases of positive results. By contrast, culture and pathology are Iabor intensive, require a few days’ turnaround time, and are much more expensive. Finally, as the test is produced on the premises, the cost per unit, including technical time, is negligible (CDN $0.55). Future methods of I-l. &~i detection will also likely include the polymerase chain reaction (Hammar et al., 19921, which could have an impact on the diagnosis and treatment follow-up of the infection.
REFERENCES Barthel JS, Everett ED (1990) Diagnosis of C~?~~yZ~~~c~~~ pylovi infections: the “gold standard” and alternatives. Rev Infect Dis 12(Suppl l)S107-114. Blaser MJ (1992) Helicobncter pylovi: its role in disease. CIilz hfect Dis 15:386-393. Brown KE, Peura DA (1993) Diagnosis of ~elieo~~~fer infection. G~s~roeilfer~ZClin ~~rf~z Am 22105115.
~~l(J~j
Chodos JE, Dworkin BM, Smith F, Van Horn K, Weiss L, Rosenthal WS (1988) C~tnpylobncfcr yylovi and gastroduodenal disease: a prospective endoscopic study and comparison of diagnostic tests. Am { Gnstvoentevol 83: 1226-1230. Cutler AF, Scubert tests to terology
Havstad S, Chen KM, Blaser MJ, Perez-Perez GI, TT (1995) Accuracy of invasive and noninvasive diagnose Helicobrzctev yylori infection. Gnstroen109:136-141.
Daniel W (1991) Hypothesis testing. In Biostntistics: A Fouw dafiou for Amlysis in flze Health Sciences. Ed, W. Daniel. New York: Wiley, pp 191-273. Gray SF, Wyatt Jl, Rathborne BJ (19863 Simplified techniques for identifying Camyylobncteu yyloridis. J Clirt Pnthol 39:1279. Hammar M, Tyszkiewicz (1992) Rapid detection
T, Wadstrom of Helicobncter
T, O’Toole PW pyIori in gastric
biopsy material by polymerase Micro&o1 30:54-58.
chain reaction.
1 Cliu
Jenicek M (1995) Clinimetrics and diagnosis. In Epidemiology: the Logic of Modem Medicine. Ed, M. Jenicek. Montreal: Epimed, pp 81-115. Marshall BJ, Warren JR (1983) Unidentified curve bacilii on gastric epithelium in active chronic gastritis. Lafzcef i: 1273-l 275. Morris A, Ali MR, Brown I?, Lane M, Patton K (1989) Cnmyylobncter pylori infection in biopsy specimens of gastric antrum: laboratory diagnosis and estimation of sampling error. 1 Clitz Pafhol 42:727-732. Murray DM (1993) Clinical relevance of infection by Helicobacter yylori. Clitr Microbial Newsleft 1533-37. Parsonnet J, Hansen S, Rodriguez L, et al. (1994) Helicobacfev pylori infection and gastric lymphoma. N El@ I Med 330:1267-1271. Peura DA (1995) He~~cu~f7cfe~p~lori: a diagnostic dilemma and a diIemma of diagnosis [editorial]. G~sfroe?z~eyo~o~~/ 109:313-315. Westblom TU, Madan E, Kemp J, Subik MA (1988) Evaluation of a rapid urease test to detect Cmzpylobncter pjylori infection. 1 Clilz Microhiol 26:1393-1394.
BACTERIOLOGY
A New Urea Broth-Based Test to Detect Helicobacter pylori Presence in Upper Gastrointestinal Biopsies Karl Weiss, Louise Poirier, Michel LaverdiPre, and Slobodan Ducic
The aim of this study was to evaluate the performmce of a simple and inexpensive komemade urea test (U-test) to defect Helicobacter pylori in upper digestive tract biopsies. We tested and compared the U-test with fkree other diagnostic methods: the C/o-test, and culture and pafkology in 110 patients randomly chosen at the endoscopy clinic. Wken using culture and/or pathology as the “gold standard,” H. pylori ZLVZS foundto exist in 54 patients. Pathology zoas positive in
50 cases (92.5%), culture iri 49 (90.7%), fke U-test in 45 (83.3%), and the C/o-test in 43 (79.6%). With regard to culture pathology, the sensitivities of the U-test and the Clo-test zoere 83.3% and 79.5%, respectively. Specificity was 200% for both methods. The K coefficient calculation between fke U-test and the Clo-test was 0.98. Tke results skozv that tke U-test is a reliable, fast, and inexpensive method for defecting H. pylori in upper gastrointestinal biopsies.
INTRODUCTION
Others such as serology are useful for epidemiologic studies but are not suitable for rapid diagnosis and for monitoring patient’s response after treatment (Barthel et al., 1990; Brown et al., 1993). Helicobacter pylori is known to produce one of the strongest bacterial ureases. This enzyme has the ability to split urea into ammonia and bicarbonates, thus creating an alkaline medium. The Clo-test (Delta West, Bentley, Australia) is a rapid, accurate, and easy to use detection method based on this enzymatic property (Brown et al., 1993; Cutler et al., 1995). Nevertheless, its cost is quite expensive in Canada, which prohibits extensive use of this diagnostic test. By using the same chemical principle, we designed a homemade urea broth test (U-test) for detecting the presence of H. pylori in upper gastrointestinal biopsies. The aims of this study were, first, to develop a rapid, easy to use, and inexpensive test (U-test) for H. pylori detection in upper gastrointestinal biopsies; and second, to compare this test with the Clo-test, as well as with two other detection methods used as the “gold standard” (culture and pathology).
Since 1983, peptic ulcer disease and gastritis have been strongly associated with the presence of Helicobatter pylori in the upper digestive tract (Blaser, 1992; Marshall et al., 1983; Murray, 1993). Several laboratory methods are used nowadays to detect the bacteria presence. Some investigative techniques such as the breath test, although noninvasive and sensitive, are cumbersome, use radioactive material, and require specialized equipment (Brown et al., 1993).
From the Department of Medical Microbiology and Infectious Diseases, HBpital Maisonneuve-Rosemont (K.W., L.P., M.L.), and the Department of preventive Medicine (S.D.), UniversitC de MontrPal, Montreal, Quebec, Canada. Address tqwint requests to Dr. K. Weiss, Department of Medical Microbiology and Infectious Diseases, HBpital MaisonneuveRosemont, 5415 l’Assomption, Montreal, Quebec Canada HIT 2M4. This study was presented in part at the 19th International Congress of Chemotherapy, 1995, Montreal, Canada (abstr no. 1106). Received 2.6 September 1995; revised and accepted 20 December 1995.
DIAGN MICROBIOL INFECT DIS 1996;24:61-64 0 1996 Elsevier Science Inc. 655 Avenue of the Americas, New York, NY 10010
0732.8893/96/$15.00 SSDI 0732-8893(95)00274-X
62
K. Weiss et al.
MATERIALS Population
AND METHODS
son, Cockeysville, MD, USA) and a Skirrow agar, which were incubated at 37°C for 7 days in a microaerophilic environment (85% N2, 10% CO,, 5% O,), obtained by adding a gas-generating pack (Camp$obacfer microaerophilic system; Difco) in a 2.5~liter sealed jar. Quality control of the microaerophilic atmosphere was assessed using a collection H. pylovi strain obtained from the Quebec provincial laboratory, plated on Brucella blood agar. Helicobacfer pylovi identification was achieved by performing a Gram stain and catalase and cytochrome oxidase reactions on isolated colonies. Furthermore, urease activity was detected by inoculating Christensen’s urea agar.
Studied
A total of 110 adult patients, referred to our endoscopy clinic for various gastrointestinal symptoms from February 1994 to March 1995, were randomly chosen and prospectively included in the study. Clinical preendoscopic diagnosis included gastritis, peptic ulcer disease, and nonulcer dyspepsia. For each patient, four 3-mm antral biopsies were taken close together, and the presence of H. pyIovi was systematically detected by four different methods: pathology, culture, Clo-test, and U-test.
Diagnostic
Pathology Warthin-Starry and Giemsa stainings were systematically done on each biopsy by the pathology department. Moreover, an immunoperoxidase-based detection method (Dako, Glostrup, Denmark) was added to the routine workup for the purpose of this study.
Tests
U-Test Our homemade test was prepared by adding 5 g of urea (Difco, Detroit, MI, USA) to 50 ml of distilled water. The pH was subsequently adjusted to 6.8, and 0.5 ml of the solution was added into individual plastic vials. One drop of a 6% phenol red solution (Difco phenol red broth base: 0.9 g in 15 ml of distilled water) was then added to the vials as a pH indicator. Once prepared, each batch was kept refrigerated in the endoscopy clinic at 4°C. On average, vials were used within 2 months after preparation. Before being used, the test material was warmed to room temperature. Biopsy specimens were put directly into the vials and left at room temperature. A positive reaction was defined as a color change of the medium within 2 h, from pale beige to purple-pink. For every batch, quality control was assessed by randomly inoculating a vial with a loopful of an H. pylovi strain obtained from the Quebec Provincial laboratory. Thereafter, every week a quality control test was performed on a randomly selected refrigerated vial.
Clo-Test This test was used according to the manufacturer’s instructions. A positive reaction was defined by a color change of the medium within 2 h inoculation with the biopsy. By definition, a biopsy sample was considered to be positive when the presence of bacteria was detected by either culture or pathology.
Statistical Analysis Comparison between tests was done using the difference between population proportions (Daniel, 1991). P values < .05 were considered to be significant.
RESULTS
Culture Biopsy specimens, rapidly transported to the microbiology laboratory in physiologic sterile saline, were immediately minced and homogenized. They were then plated on a Brucella blood agar (Becton DickinTABLE
1
Detection of Helicobacfer Different Methods”
Diagnostic test U-test Clo-test Culture Pathology No. of patients
A total of 54 patients out of 110 had a positive upper gastrointestinal biopsy by culture and/or pathology (Table 1). For 5 patients, biopsies were positive for H. pylovi by pathology but negative on culture. Of these,
pylovi in 110 Patients by Four
Total Positive
Test Results + + + + 38
+ + + 1
“+: positive upper gastrointestinal
+ f + 4
+ _ + + 2
_ _ + + 5
_ _ + _ 3
_ _ _ + 1
_ _ _ _ 56
biopsy; -: negative upper gastrointestinal
45/54 (83.3%) 43/54 (79.6%) 49/54 (90.7%) 50/54 (92.5%) 54 biopsy.
63
Urea Test for 11. pylori
four were also positive by the two rapid methods (Clo-test and U-test). In one patient, the bacteria was detected by pathology only. There was a perfect agreement between the different histology staining techniques, and Giemsa was as good as WarthinStarry, an observation already noticed by others (Gray et al., 1986). In three patients, culture was the sole positive test; however, growth was very light, probably reflecting a small inoculum below the detection threshold of the other diagnostic methods. Overall, biopsies were positive by pathology for 50 patients and by culture for 49; in nine cases there was disagreement between the two methods. When analyzing the results obtained with the rapid detection methods, results were very comparable between the Clo-test and the U-test. Although not statistically signi~cant, the latter was even able to detect two positive biopsies, confirmed by pathology and culture, which were not detected by the former. The reverse situation did not happen. The K coefficient (Jenicek, 1995) is a useful tool for measuring the external validity of a diagnostic test. It ranges from -1 (disagreement) through 0 (random agreement), to 1 (complete agreement). In our case, when comparing the Clo-test with our U-test, we found an almost perfect match between the two methods (K = .98). All positive U-test biopsies (45) were positive by either pathology or culture, with most of them (40) positive by both methods. Among the five negative biopsies by either pathology or culture, two of the four negative cultures occurred as a cluster; this suggests a possible technical problem with the specimen processing. No sample was positive by our U-test but negative by one of the two “gold standard” diagnostic tests. When compared with culture and/or histology used as a “gold standard,” sensitivities of both tests were 79.6% and 83.3%, respectively (Tables 2 and 3). A specificity of 100% was also recorded for both tests with regard to culture and/or histology. No method was perfect in detecting all positive samples. Statistically, there was no significant difference in terms of sensitivity among pathology, culture, and the U-test. TABLE
2
Comparison of the CLO-TestTM with Culture and Histology Culture/Histology
CLO-test
+ -
+
-
43 11 54
56
67
56
110
Total Sensitivity: 79.5% CI,, (72~87.1%) Specificity: 100% CI,, (9&l-100%) CI,,: 95% confidence
interval.
0
43
TABLE
3
Comparison of the U-Test with Culture and Histology Culture/Histology + + -
U-test Total
-
45
0
9
56
65
54
56
110
45
CI,, (76.3-90.1%)
Sensitivity:
83.3%
Specificity:
100% CI,,
(98.1-100%)
CI,,: 95% confidence interval.
The only significant difference was noted between pathology and the Clo-test (P = .026).
DISCUSSION HeEicobncter pylori is an increasingly important microorganism associated with many upper gastrointestinal pathologies, including certain types of gastric cancer (Blaser, 1992; Parsonnet et al., 1994). However, many questions still have to be elucidated regarding its detection as well as treatment (Peura, 1995). Basically two types of detection methods are available: invasive methods, necessitating an endoscopy, and noninvasive methods such as the breath test. Each category of tests has its drawbacks and advantages in terms of cost, rapidity, required equipment, and potential complications for the patients (Brown et al., 1993; Chodos et al., 1988). Although requiring an endoscopy, rapid urease tests have been singled out as the most cost-effective method to detect H. pylori (Peura, 1995). The major problems associated with this technique are the cost and the potential complications of an endoscopy. However, the test itself is the least expensive detection means and gives a rapid answer for treatment purposes. We developed our own test, bearing in mind the need for a rapid method comparable in efficacy to the Clo-test. The K coefficient calculation enables us to compare the performance and the reproducibility of our test with the Clo-test. The agreement between the two rapid detection methods was almost perfect (.98), suggesting that the U-test is very comparable to the former. One difference with the Clo-test resides in the absence of any bacteriostatic agent in our test. This does not seem to affect the test performance, which is why the 2 h cutoff point was chosen. Other urea-splitting bacteria present in the digestive tract such as Proteus species were unable to give a false-positive result in that time frame. If a 24-h reading time had been chosen, sensitivities of both tests would have increased. The Clo-test positive predictive value ranges between 90% and 98%
64
K. Weiss et al.
when read at 24 h (Barthel et al., 1990). Indeed, for the study purposes, a few specimens considered negative by the two m-ease tests became positive when read at 24 h. Nevertheless, by doing this, we lost a great advantage of these rapid tests, and the possibility of having false-positive results due to other bacteria arose. With a sensitivity reaching our homemade urea 83.3% (CI,,: 76.3%-90.1%)‘ broth test is a reliable method to detect H. ~~~~~~in upper gastrointestinal biopsies. It is very comparable to what has been previously found for the Clo-test by different groups (Cutler et al., 1995; Morris et al., 1989). Other rapid urease tests with satisfactory results have been reported. In their study, Westblom et al. (1988) used a l-h cutoff point and obtained a sensitivity of 67%. Although the concept of “gold stan-
dard’ tests is debatable (Peura, 1995), culture and histology with 100% specificity are the best candidates for this description (Barthel et al., 19901, which is why we decided to choose them as points of comparison. Our U-test could be useful in an outpatientoriented setting. Treatment directed against H. p$ori can be rapidly initiated in cases of positive results. By contrast, culture and pathology are Iabor intensive, require a few days’ turnaround time, and are much more expensive. Finally, as the test is produced on the premises, the cost per unit, including technical time, is negligible (CDN $0.55). Future methods of I-l. &~i detection will also likely include the polymerase chain reaction (Hammar et al., 19921, which could have an impact on the diagnosis and treatment follow-up of the infection.
REFERENCES Barthel JS, Everett ED (1990) Diagnosis of C~?~~yZ~~~c~~~ pylovi infections: the “gold standard” and alternatives. Rev Infect Dis 12(Suppl l)S107-114. Blaser MJ (1992) Helicobncter pylovi: its role in disease. CIilz hfect Dis 15:386-393. Brown KE, Peura DA (1993) Diagnosis of ~elieo~~~fer infection. G~s~roeilfer~ZClin ~~rf~z Am 22105115.
~~l(J~j
Chodos JE, Dworkin BM, Smith F, Van Horn K, Weiss L, Rosenthal WS (1988) C~tnpylobncfcr yylovi and gastroduodenal disease: a prospective endoscopic study and comparison of diagnostic tests. Am { Gnstvoentevol 83: 1226-1230. Cutler AF, Scubert tests to terology
Havstad S, Chen KM, Blaser MJ, Perez-Perez GI, TT (1995) Accuracy of invasive and noninvasive diagnose Helicobrzctev yylori infection. Gnstroen109:136-141.
Daniel W (1991) Hypothesis testing. In Biostntistics: A Fouw dafiou for Amlysis in flze Health Sciences. Ed, W. Daniel. New York: Wiley, pp 191-273. Gray SF, Wyatt Jl, Rathborne BJ (19863 Simplified techniques for identifying Camyylobncteu yyloridis. J Clirt Pnthol 39:1279. Hammar M, Tyszkiewicz (1992) Rapid detection
T, Wadstrom of Helicobncter
T, O’Toole PW pyIori in gastric
biopsy material by polymerase Micro&o1 30:54-58.
chain reaction.
1 Cliu
Jenicek M (1995) Clinimetrics and diagnosis. In Epidemiology: the Logic of Modem Medicine. Ed, M. Jenicek. Montreal: Epimed, pp 81-115. Marshall BJ, Warren JR (1983) Unidentified curve bacilii on gastric epithelium in active chronic gastritis. Lafzcef i: 1273-l 275. Morris A, Ali MR, Brown I?, Lane M, Patton K (1989) Cnmyylobncter pylori infection in biopsy specimens of gastric antrum: laboratory diagnosis and estimation of sampling error. 1 Clitz Pafhol 42:727-732. Murray DM (1993) Clinical relevance of infection by Helicobacter yylori. Clitr Microbial Newsleft 1533-37. Parsonnet J, Hansen S, Rodriguez L, et al. (1994) Helicobacfev pylori infection and gastric lymphoma. N El@ I Med 330:1267-1271. Peura DA (1995) He~~cu~f7cfe~p~lori: a diagnostic dilemma and a diIemma of diagnosis [editorial]. G~sfroe?z~eyo~o~~/ 109:313-315. Westblom TU, Madan E, Kemp J, Subik MA (1988) Evaluation of a rapid urease test to detect Cmzpylobncter pjylori infection. 1 Clilz Microhiol 26:1393-1394.