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Published: August 2010Print Record of Viewing
Dr. Hata provides an overview of Helicobacter pylori, and discusses considerations you should be aware of for optimal diagnostic testing.
Presenter: D. Jane Hata, PhD
Welcome to Mayo Medical Laboratories' Hot Topics. These presentations provide short discussions of current topics and may be helpful to you in your practice.
Our presenter for this program is Dr. Jane Hata, Director of the Clinical Microbiology Laboratory, Department of Laboratory Medicine and Pathology at Mayo Clinic in Jacksonville, Florida. Dr. Hata will provide an overview of Helicobacter pylori, and discuss considerations you should be aware of for optimal diagnostic testing.
Today, we will discuss the history of Helicobacter pylori, some unique characteristics of the organism and its role in pathogenesis in human disease.
In addition, I would like to discuss a variety of tests available in the clinical laboratory, and finish with current recommendations as to how these tests can best be applied for initial diagnosis and monitoring of patients during and after treatment of Helicobacter pylori infection.
Helicobacter pylori is actually a very fascinating and unique organism. Helicobacter sp. inhabits the hepatobiliary and gastrointestinal tracts of birds and mammals, and survives within the mucous gel layer adjacent to the gastric epithelia in the cardia, corpus, and antrum of the human stomach.
As its name suggests, it is indeed a spirochete, assuming either a spiral, or a curved bacillary shape. It is approximately 0.3 to 1.0 micrometers wide by 1.5 to 10 micrometers long.
It will stain in a gram-negative fashion, and exhibit motility via bipolar flagella.
In the laboratory, Helicobacter survives best at 37 degrees centigrade, and at oxygen concentrations of 5% to 10%; thus it is microaerophilic. It is also hypercapnic, requiring carbon dioxide concentrations between 5% and 12%.
Useful to our identification schemes is the fact that it is oxidase positive, and exhibits a very strong urease activity.
The discovery of Helicobacter pylori’s association with peptic ulcer disease is a story in itself.
In 1984, a research group, led by Dr. Barry Marshall at Fremantle Hospital in Australia, proposed that what were then known as “pyloric Campylobacter” were indeed associated with peptic ulcer disease. The thought that a bacterium could survive the pH of the stomach and cause a specific disease entity was seen as a very controversial view at the time, and resulted in a great deal of criticism over the validity of Marshall’s work.
Dr. Marshall even went so far as to prove Koch’s postulates by drinking a suspension of Helicobacter pylori prepared in his laboratory. After 2 weeks, he developed dyspepsia and peptic ulcer disease. Helicobacter pylori was then isolated from endoscopic samples from his own stomach, thus completing Koch’s postulates.
Consequently, in 1994, the National Institutes of Health concluded that Helicobacter pylori was a causative factor in 90% of peptic ulcer disease and warranted treatment with antibiotics. Despite the earlier controversy, Dr. Marshall was ultimately vindicated; and received the 2005 Nobel Prize in Medicine.
Humans are the primary vectors for Helicobacter pylori transmission. This may occur through:Fecal/oral Oral/oral, or Gastric/oral contamination
Household transmission of Helicobacter pylori gastroenteritis may occur, particularly in households with small children. Other epidemiologic factors shown to contribute to transmission include household crowding, low income, genetic predisposition, lifestyle, and other socioeconomic factors.
An estimated 25 percent of US children between 6 and 19 years old are infected with Helicobacter pylori. Infections may be asymptomatic, and infection rates increase with age. Overall, the seropositivity rate among US adults is estimated to be approximately 32.7%.
As first demonstrated by Dr. Marshall’s work, exposure to an infectious dose of Helicobacter pylori can result in an acute gastritis, with abdominal pain, nausea, and vomiting within 2 weeks of exposure.This can progress to chronic gastritis, with concomitant duodenal inflammation and development of gastric ulcers. Persistent inflammation due to Helicobacter pylori infection is considered a risk factor for eventual development of gastric adenocarcinoma.
In 2007, the American College of Gastroenterology updated its guidelines for the diagnosis and management of Helicobacter pylori infections. Because of the proven linkage between Helicobacter pylori infection and peptic ulcer disease, these guidelines defined indications for diagnostic testing in patients with:Active peptic ulcer disease A past history of documented peptic ulcer Gastric mucosa associated lymphoid tissue, or MALT lymphoma, a history of gastric cancer, or a relative with gastric cancer
However, it should be said that in the presence of outright alarm features; GI bleeding, anemia, weight loss, persistent vomiting, the patient should proceed directly to endoscopy with accompanying histological studies. Testing for Helicobacter pylori and treatment of positives is an approved approach due to increased healthcare costs; approximately 6 billion dollars a year, and loss of productivity in individuals with peptic ulcer disease and Helicobacter pylori infection. For dyspeptic patients <45 years old, a noninvasive Helicobacter pylori test, and treatment, if positive, is recommended.
Although we will not extensively discuss treatment during this presentation, a regimen of a proton pump inhibitor, clarithromycin, amoxicillin, or metronidazole for 14 days is generally indicated. Bismuth may also be added to increase efficacy of the treatment regimen.
Now, let’s move into the final portion of today’s presentation, which will be a discussion of various testing modalities for Helicobacter pylori. A list of tests offered by Mayo Medical Laboratories will be available at the end of this presentation.
Specific testing should only be performed on patients who are symptomatic; asymptomatic colonization with Helicobacter pylori can occur and cause confusion in diagnosis.
As we will discuss in a moment, tests can be divided into those that do, and do not, require invasive endoscopy. A single gold standard test for diagnosis of Helicobacter pylori infection does not exist.
Instead, we rely on selection of tests in combination with:Clinical presentation of the patient Pretest probability of infection The availability of the test, and the cost of the test
In order to assure an appropriate selection, it is important to understand the strengths and weaknesses of each of the tests that we will discuss.
Diagnostics of Helicobacter pylori infection can be divided into 2 groups:Invasive; and Noninvasive testing
Let’s first discuss invasive testing, which is based on the use of endoscopy and employs Histology, Rapid Urease testing, and Culture.
Endoscopy is recommended as a primary diagnostic method for:Any symptomatic patient 45 years or older Any patient with alarm features
A biopsy specimen obtained during endoscopy will be used for special staining and pathology interpretation. A Gram stain, acradine orange, Giemsa, silver stain, or immuno stains may be used for direct visualization of Helicobacter pylori bacteria.
Endoscopy has >95% sensitivity and specificity, with multiple biopsies resulting in even greater accuracy. The downside is that this is an invasive procedure, it is expensive, and specific expertise is required. Sensitivity of endoscopy can be affected by proton pump inhibitors, bismuth, or antibiotics, thus, this test cannot be used during treatment of the patient.
The rapid urease test, also known as the CLO test, is based on a biopsy sample placed on either a reaction strip or agar gel containing urea, a buffer, and a pH indicator. The urease activity expressed by Helicobacter pylori will cause a change in the color of the pH indicator in the case of a positive test. This is a rapid test, relatively inexpensive, and sensitive in correctly selected patients. Results can be interpreted within 3 hours, although the CLO test may be held up to 24 hours.
Proton pump inhibitors, antibiotics, and bismuth will affect the result of this test, resulting in false-negatives. The rapid urease test is not recommended for patients who are currently receiving therapy for Helicobacter pylori infection.
It is possible to culture Helicobacter pylori from biopsy specimens, although it should be stated that this is not a routine procedure. Culture is not routinely used for initial diagnosis; it is not as sensitive as histology and the rapid urease test. Culture is necessary for susceptibility testing if treatment failure is suspected.
Specific conditions to support the growth of this organism are required. As a rule, growth occurs at:5 to 7 days if culture plates are held at 37 degrees 5% to 10% oxygen and 5% to 12% carbon dioxide with humidity.
The use of either Brucella agar supplemented with 5% horse blood, or brain heart infusion media with 7% horse blood has been most successful for growth although recovery using Campylobacter, Chocolate, Mueller-Hinton, and Wilkins-Chalgren medias has been reported.
If culture conditions are met, you will see grey, translucent colonies with swarming.
Remember, colonies will be urease, oxidase, and catalase positive. These characteristics, plus a negative hippurate test will distinguish Helicobacter pylori, from another enteric organism, Campylobacter jejuni.
Let’s now turn our attention to those tests that are noninvasive.Urea breath test Serology Fecal antigen test
The Urea Breath test takes advantage of the strong urease activity expressed by Helicobacter pylori.
In this test, the patient will ingest carbon 13- or carbon 14-labeled urea either via capsule or a flavored liquid. The labeled urea then diffuses thru the mucosal gel layer of the gastric epithelia in which the Helicobacter reside. The Helicobacter pylori splits the ingested urea into ammonia and labeled carbon dioxide via their urease activity.
Carbon dioxide is then exhaled. A sample of exhaled breath is collected and measured in a scintillation counter or infrared spectrophotometer in order to measure the amount of labeled carbon dioxide. This is an indirect measure of urease activity and subsequent presence of Helicobacter pylori.
The urea breath test is very sensitive and specific; both exceeding 95%. Although the patient is ingesting radioactive carbon, the exposure is quite low, equal to the daily background dose. Nonetheless, the urea breath test is not FDA approved for use in children under the age of 8.
Like the CLO test, the sensitivity of the urea breath test can be affected by proton pump inhibitors, antibiotics, or bismuth. Thus, it is of limited utility if the patient is currently under treatment for Helicobacter pylori infection.
The urea breath test is expensive. As it is based on measurement of radioactivity, it does require specialized equipment for measurement of the carbon dioxide analyte and infrastructure to manage radioactive materials. Additionally, the performance characteristics of this test have not been established for children <18 years old. Other testing alternatives may be more suitable for this patient population.
ELISA testing can be used for the serological detection of both IgM and IgA produced in response to infection with Helicobacter pylori. IgM develops approximately 21 days after infection and is detected at higher levels during a primary active infection. However, compared to other noninvasive tests, serology for IgM and IgA is of relatively low sensitivity and actually has limited clinical utility.
Detection of IgA may be slightly more specific in children, compared to IgM, but overall test sensitivity is only approximately 70%.
Detection of IgM can be used for screening of symptomatic individuals for acute Helicobacter pylori infection, but since peptic ulcer disease is due to chronic Helicobacter pylori infection, this test is of limited clinical utility.
Of all the serological tests, the enzyme linked fluorescence assay (ELFA) for IgG has the best overall sensitivity and specificity. Detection of IgG is most useful for screening symptomatic individuals for Helicobacter pylori infection, as compared to IgM and IgA. IgG detection can be performed concurrently with proton pump inhibitor treatment. Serum samples are relatively easy to obtain. However, since IgG levels may remain positive for up to a year, this test cannot be used for detection of eradication of Helicobacter pylori infection.
If you are considering use of a serological test for Helicobacter pylori, you may want to consider the following:
Does positive serology require additional testing for confirmation of Helicobacter pylori infection before treatment is started?
In answering this question, this is a situation where one needs to be aware of the advantages and disadvantages of the various types of tests used for detection of Helicobacter pylori.
False-positive serology tests are more common in low prevalence populations. Here is a graph which shows the effect of Helicobacter pylori prevalence on the positive predictive value, a positive test in the presence of disease, for a serological test.
According to Bayes’ theorem, when the prevalence of disease is low, most results are falsely positive. If you use the US seropositivity prevalence of 32.7%, the graph tells us the positive predictive value of a serology test would be just over 50%. If your community has a Helicobacter pylori prevalence of 20%, which is the case of much of the United States, the positive predictive value of a serological test will be less than 40%. Subsequently, the American College of Gastroenterology does not recommend use of serology in low prevalence populations.
To answer our question, if you do choose to utilize a serological test for Helicobacter pylori, because of issues with low positive predictive values, positive results should be confirmed with a noninvasive test that identifies active Helicobacter pylori infection, such as the urea breath test or the fecal antigen test.
We’ve discussed the urea breath test, what about the fecal antigen test?
This test utilizes an enzyme immunoassay format, with multiple monoclonal antibodies to detect Helicobacter pylori antigens. Earlier versions of this test, which used polyclonal antibodies, were not as sensitive. The use of monoclonal antibodies have improved the sensitivity of this test to >90%, both before and after treatment. The fecal antigen test is more accurate than serology in populations with a low pretest probability of Helicobacter pylori infection. This test should not be used during treatment of Helicobacter pylori infections, as sensitivity is affected by use of proton pump inhibitors, antibiotics, bismuth, or if the patient has an actively bleeding ulcer. This test does require collection of a fresh stool sample; some patients may be averse to this. The fecal antigen test can be used 4 weeks after completion of treatment to assess success. It is an alternative to the urea breath test for this purpose.
Let’s briefly explore how one can best assess eradication of Helicobacter pylori infection after completion of a course of treatment.
As we have discussed, this can be confirmed by noninvasive means, either the urea breath test, or the fecal antigen test. Neither of these tests should be performed less than 4 weeks after completion of a treatment regimen. Due to persistence of antibody, a serological test is not recommended to assess cure.
If the urea breath test or fecal antigen test are still positive, or if the patient is still symptomatic after treatment, endoscopy is indicated so that pathology evaluation, and culture of biopsy samples for Helicobacter pylori can be performed.
Culture is necessary if antibiotic susceptibility testing is under consideration.
Here is an algorithm located at the link indicated on the slide that summarizes the types and best usage of tests for detection of Helicobacter pylori that we have discussed today.
So, to summarize today’s discussion:
Helicobacter pylori affects 30% to 40% of the US population, but prevalence in most US communities may be closer to 20%.
The approach of test and treat if the patient is symptomatic is strongly recommended. If alarm features are present, endoscopy with histology and rapid urease testing should be performed.
In patients with dysphagia, or other pertinent clinical indications, noninvasive tests such as the urea breath test or fecal antigen test are the preferred approach. These tests cannot be used during treatment; they can be used 4 weeks after completion of treatment.
Serology can be used to detect acute infections, and can be used during treatment, but overall sensitivity and specificity are much lower than the urea breath test and fecal antigen tests. Serology cannot be used to assess Helicobacter pylori eradication.
This concludes today’s discussion of Helicobacter pylori and considerations for diagnostic testing.
Here is a list of the Helicobacter pylori tests currently available from Mayo Medical Laboratories.