Invasive Tests

Histopathological examination of gastric biopsy specimens. Helicobacter spp. can be detected in histological preparations of gastric biopsy specimens stained with a variety of methods. Hematoxylin and eosin is a suboptimal choice of stains for the specific task of detecting H.pylori. Reliable special stains include the Warthin-Starry and the Steiner silver stains, the Giemsa, Diff-Quick, and Gimenez stains, and a triple stain, which, by combining modified Steiner staining, hematoxylin and eosin, and Alcian blue, allows the simultaneous visualization of the features of gastritis, including intestinal metaplasia, and the bacteria. Several modified versions of this stain have become available. Anti– H.pylori antibodies for the immunohistochemical detection of H.pylori in paraffin-embedded biopsy specimens have high sensitivity and specificity; some laboratories use them for routine clinical diagnosis.

In situ hybridization and polymerase chain reaction. In situ hybridization may be used for the detection of H.pylori in paraffin-embedded sections, but high cost and technical difficulties have relegated this procedure to the research laboratory. Polymerase chain reaction for the detection of H.pylori infection must also be considered a research tool because of its requirement for a sophisticated molecular biology laboratory, the availability of appropriate primers, and its high price.

Smear, brush, and touch preparations. Smears of gastric mucus and exfoliated epithelial cells, usually with Gram staining, may allow the detection of bacteria within minutes of the endoscopic procedure. Rapid urease tests have made cytologic assays obsolete.

Bacterial culture.H.pylori is best cultured in a microaerophilic and humid atmosphere on culture media requiring fresh horse or sheep blood and antibiotics to suppress contaminants. Cultures for H.pylori are technically more complicated than those performed by the usual clinical microbiology laboratory. Because many clinical facilities are not equipped to perform the time-consuming procedures necessary to culture H.pylori, several methods for transportation have been devised.

Rapid urease tests. These assays exploit the high content of urease of H.pylori. A fragment of gastric mucosa is placed into a broth or in agar containing various concentrations of urea. The urease produced by H.pylori hydrolyzes the urea and releases ammonia, which raises the pH of the broth or agar, and an appropriate indicator (e.g., phenol red) changes color as the pH increases. In the first commercially produced rapid urease test, the CLOtest, the original yellow gel capsule into which the specimen is placed becomes red within minutes to hours, depending on the quantity of bacteria present. Several rapid urease tests are now commercially available. Both their specificity and sensitivity, compared with histopatho­logical examination, are extremely high, in most cases approaching 100%.

Noninvasive Tests

Serology. The development of new techniques has minimized the problems of cross-reactivity that plagued first-generation serologic tests. Currently available tests are highly reliable. The large numbers of studies aimed at the discovery of an optimal diagnostic test for H.pylori infection have also provided valuable information on the immune responses to this organism. For example, the selection of H.pylori strains as sources of antigen is critical to the specificity and sensitivity of a test, and it is imperative to evaluate specific tests in the population to which it would be applied before selection of a test for use in specific settings. This population specificity highlights the importance of the many different geographic strains that infect different world populations.

Simplified “in-office” immunoenzymatic tests. Several in-office devices have been developed for the rapid detection of IgG anti– H.pylori antibodies. Most of them consist of disposable kits that provide a yes/no answer within a few minutes of placing a drop of serum in a well that is preabsorbed with antigen and an immunoenzymatic detection system. Although some of these tests are accurate, results have been generally less than the minimum required sensitivity and specificity of 90%. Antibodies (mostly of the IgG class) against H.pylori have been detected in the saliva and the urine of infected patients. The specificity and sensitivity of urine tests have been found to be satisfactory in several studies, particularly in Japan.

Stool antigen assay. An enzymatic immunoassay (HpSA) that detects H.pylori antigens in stools (thus providing information on the presence of current infection) has become available for the diagnosis of H.pylori infection and for monitoring the response to therapy. The test is similar to an enzyme-linked immunosorbent assay, using polyclonal anti– H.pylori antibody absorbed to microwells. A large European multicenter study has yielded encouraging results.

Urea breath tests. The urea breath tests are among the most important and innovative methods to detect H.pylori infection. These tests rest on the ability of H.pylori to produce large quantities of urease. The ingestion of a solution containing urea is rapidly followed, in an infected patient, by the production of ammonia and carbon dioxide. The latter rapidly appears in the subject’s breath. If the ingested urea is labeled either with the radioactive isotope 14C or with the nonradioactive isotope 13C, then the exhaled carbon dioxide will also be labeled and, therefore, measurable by an appropriate detection method. When 14C-labeled urea is used, the general method consists of the ingestion of a solution or a capsule containing quantities between 0.5 and 10 µCi of the isotope-labeled urea. When 13C-labeled urea is used, test subjects are given a solution of 125 g of 99.9% labeled urea followed by a meal aimed at increasing its permanence in the stomach. After a period of time, the subject inflates a balloon, which is immediately sealed and sent to a laboratory for the detection of the isotope-labeled carbon dioxide. Both types of tests are now well standardized and are approved by regulatory agencies in Europe and North America. The urea breath tests are extremely sensitive and specific and, in contrast to serologic tests, detect current active infection (not evidence of past infection). Their widespread use has made them more affordable, and they have become the test of choice for a variety of populations, including children, pregnant women, and patients who cannot undergo an endoscopic procedure.

Helicobacter heilmannii Infection

More than 35 species of Helicobacter have been described, but only few other than H.pylori have been shown to cause gastritis in humans: H felis, H fennelliae, H cinaedi, and H heilmannii. Among these, H heilmannii (formerly known as Gastrospirillumhominis) is the most common, with an estimated prevalence of approximately 1% of all human Helicobacter infections. In some rural areas in Eastern Europe, this organism has been detected more commonly, leading to the hypothesis of zoonotic transmission. The bacterial morphology is characteristic: organisms measure 5 to 9 µm in length (twice as long as H.pylori) and have five to seven spirals clearly visible with a silver stain. Gastritis caused by H heilmannii is often milder and more patchily distributed than H.pylori gastritis. The inflammation tends to be more circumscribed and to affect mostly the antrum, although cases with severe corpus active inflammation are seen. Concurrent erosions and ulcers have been reported to be less common than in H.pylori gastritis. The diagnosis rests on the recognition of the bacterial morphology, although the distinction between H heilmannii and H felis is not possible by light microscopy.

Treatment of Helicobacter pylori Infection

At present, the only universally agreed on indications for treatment are H.pylori–related duodenal and gastric ulcers and low-grade, primary B-cell MALT lymphoma. H.pylori should be eradicated in patients with documented ulcer disease, whether or not the ulcers are currently active, to reduce the likelihood of relapse. Most clinical trials do not provide convincing data in support of the benefits of eradication of infection in patients with nonulcer dyspepsia, and there are no controlled studies showing that eradicating H.pylori from a population will reduce the incidence of gastric cancer. For various logistical and ethical reasons, it is unlikely that such trials will be ever carried out to the satisfaction of those who demand unequivocal evidence. The most pressing question then is whether we should hold back and wait for more data or act now based on current information. Today, there is ample epidemiologic and biologic evidence that whereas H.pylori gastritis may not be the only cause of the development of atrophy and intestinal metaplasia, it almost always provides the necessary background on which these lesions arise. By treating H.pylori gastritis, we can prevent the development of atrophy and metaplasia, and most likely we would also arrest the progress of these lesions in infected persons who have already developed them. As a result, we should be able to prevent millions of gastric cancers. The incidence of non–NSAID-induced peptic ulcers would also be greatly reduced, and primary gastric lymphomas would all but disappear. Thus, we ought to put aside the teleological questions on the ultimate significance of our immemorial amphibiotic relationship with H.pylori and its intriguing evolutionary and metaphysical implications and proceed to cure infected patients.

In vitro, H.pylori is susceptible to a wide range of antibiotics, but monotherapy has been disappointing in vivo, probably because of inadequate antibiotic delivery to the sites of colonization. Thus, several multidrug regimens have been developed, the most successful of which are triple and quadruple combinations that achieve H.pylori eradication rates of more than 90% in many trials and more than 75% in clinical practice. The most commonly used 7- and 14-day drug regimens consisting of a proton pump inhibitor and two or three antimicrobial agents. The major determinants of therapeutic failures are inadequate patient compliance and drug resistance, particularly to metronidazole and clarithromycin.

There are no established guidelines for posttreatment testing. When eradication therapy is given for gastric ulceration or MALT lymphoma, there is an opportunity to retest for H.pylori at repeat endoscopy, which is performed to evaluate healing or regression. For duodenal ulceration, a urea breath test, a stool antigen test, or an endoscopy with gastric biopsy should be performed 4 to 6 weeks after treatment. When therapy is administered to treat asymptomatic infections, posttreatment testing is generally not deemed necessary.

Evolution and Associations of Helicobacter pylori Gastritis

H.pylori gastritis is a life-long infection that can be viewed as a spectral disease. At the one end of the spectrum, inflammation remains mostly confined to the antrum and the cardia, the oxyntic mucosa is mildly affected, and atrophy is absent or minimal. At the other end, severe inflammatory changes involve the entire gastric mucosa and inflict progressive damage that results in loss of the normal gastric glands and their replacement by fibrous tissue and metaplastic epithelia. Although these are aspects of the same disease that can be placed on a continuous scale, the epidemiologic distribution and the associations of the two extremes are profoundly different. Gastritis confined to the antrum and without significant atrophy does not impair acid secretion, is commonly present in patients with duodenal ulcer, and has not been linked to increased cancer risk. Conversely, generalized gastritis with atrophy reduces acid secretion and is strongly associated with gastric adenocarcinoma. Thus, for the practical purposes of classification and prognostic evaluation, it has been expedient to divide gastritis into two phenotypes: nonatrophicantrum-predominant gastritis and multifocal atrophic gastritis.

Antrum-Predominant Gastritis This is the most common form of gastritis in the Western world. Its characteristics are as follows: a moderately to severely inflamed antrum; a mildly inflamed or normal corpus; minimal or absent atrophy or intestinal metaplasia, limited to the antrum; and normal or increased acid secretion. Most patients with this type of gastritis have neither symptoms nor complications. However, they have a risk of duodenal ulcer, estimated at 20% over their lifetime.

Atrophic Gastritis Also called multifocal atrophic gastritis, metaplastic atrophic gastritis, and atrophic pangastritis, this disorder is characterized by marked diffuse mucosal inflammation, often more severe in the oxyntic mucosa, by patches of atrophy and intestinal metaplasia in both antrum and corpus, and by variously reduced acid secretion. Atrophic gastritis is most prevalent in populations that are—or were, until a few decades ago—living in suboptimal sanitary conditions, including much of South and East Asia, Latin America, and parts of Central, Eastern, and Southern Europe. Socioeconomic factors may be a surrogate for other unknown agents that modulate the evolution of gastritis, because there are notable epidemiologic exceptions to this association. Japan, a country with high levels of sanitation and personal hygiene, has one of the world’s highest prevalences of atrophic gastritis and a high incidence of gastric adenocarcinoma. In contrast, Equatorial Africa, in spite of its precarious socioeconomic texture, inadequate sanitary standards, and a prevalence of H.pylori close to 90%, appears to have a low prevalence of atrophic gastritis and a low incidence of gastric adenocarcinoma. Several explanations have been proposed for this ‘African enigma,” ranging from diet, human and bacterial genetics, to unreliable statistics. Atrophic gastritis is a risk factor for gastric epithelial dysplasia, a precursor of the intestinal-type adenocarcinoma of the stomach. It also predisposes patients to gastric ulcer.

Peptic Ulcers, Carcinoma, and Lymphoma In addition to peptic ulcer disease and gastric carcinoma, H.pylori infection is also epidemiologically related to primary gastric MALT-lymphomas.

Extragastrointestinal Manifestations of Helicobacter pylori infection H.pylori infection has been proposed to be associated with an ever-growing number of extragastric manifestations of H.pylori infection, even if their causal relationship with H.pylori is far from conclusively demonstrated. Most of these associations are founded on epidemiologic data; however, both H.pylori infection and of some of the conditions allegedly associated with it (e.g., atherosclerosis) have a very high prevalence in many populations. Thus, biologic rather than epidemiologic data will be needed to prove causation. For one of these conditions, rosacea, there are several randomized trials that essentially disprove the association with H.pylori. Conversely, several clinical studies based on treatment results lend some support to the possibility of a pathogenetic involvement of H.pylori in iron deficiency anemia and autoimmune thrombocytopenic purpura. For most other conditions, data are insufficient to reach informed conclusions; however, the biologic plausibility in some of the proposed associations (e.g., with migraine) is so low that one must wonder whether attempts to prove causality are worth the effort.