Laboratory diagnosis of Helicobacter pylori
Laboratory diagnosis of Helicobacter pylori
Introduction
Helicobacter pylori is a gram-negative, curved, and microaerophilic bacillus. The bacterium is now known to be a major cause of chronic gastritis, peptic ulcers (in both the duodenum and stomach), adenocarcinoma, and lymphoma of MALT cells.
The infection caused by this bacterium is universal and can be seen in all age groups.
It is estimated that about 50% of the world's population is infected. Unlike in developed countries, in developing countries, humans became infected with the bacterium in the early years of their lives, and the infection was transmitted through digestion by swallowing bacteria, but there was also the possibility of transmission from person to person H. pylori because of familial spread. Infection occurs.
But the most important way is through water.
Clinical findings
Acute infection can lead to disease in the upper gastrointestinal tract, which is accompanied by pain and nausea, and in some patients may include vomiting and fever.
These symptoms last for one to two weeks, and after H. pylori settles, the infection persists for years and possibly decades or even a lifetime.
Infection with this bacterium is usually chronic in adults and does not improve without drug treatment, but spontaneous removal of the bacterium has been seen in children.
Gastritis caused by this bacterium leads to complications such as gastric ulcer (lower stomach or anther area), duodenum, gastric mucosal atrophy, carcinoma and lymphoma of gastric MALT cells.
The most common form of gastritis caused by this bacterium is the dominant gastritis in the gastric anther area. In contrast, there are patients with predominant gastritis in the gastric trunk area that results in multi-focal atrophy. These patients are prone to stomach ulcers, gastric atrophy, intestinal metaplasia, and finally gastric carcinoma.
The risk of peptic ulcer is high in people with H. pylori infection, and eradication of this bacterium significantly reduces the risk of recurrence of H. pylori-induced peptic ulcer. The bacterium was identified in 1994 as a first-class carcinogen for gastric cancer.
The role of H.pylori in non Ulceric Dyspepsia is unclear, but H.pylori in these patients
It is very common. The genetic predisposition of the host is also important in causing infection caused by this bacterium.
Helicobacter pylori, which is specific to dogs, cats and pigs, can also cause mild gastritis in humans.
Pathogenesis
The pathogenic factors of this bacterium are:
Mobility (this bacterium has 7-3 coated flagella in one pole and is highly mobile. These flagella have the ability to pass bacteria through the gastric mucosa), urease enzyme (this plasma urea enzyme secreted by the wall). Decompose the stomach,
It releases ammonium ions, which can neutralize the pH of the environment around the bacteria, and on the other hand, the ammonia itself can directly damage epithelial cells), adhesion (proteins such as hemagglutinin and Bab A protein, which cause adhesion). The bacteria enter the lining cells of the gastric mucosa),
Cytotoxin (vacuole vacuole cytoxoxin, which damages gastric mucosal cells, increases cell permeability to urea to increase urea flow through the gastric mucosa and, by damaging the mitochondrial membrane, secretes cytochrome C). It in turn initiates the process of apoptosis or cell death in gastric mucosal cells).
Host safety response to H.pylori
Helicobacter pylori infection can lead to persistent inflammation of the stomach in all infected people, but this bacterium is non-invasive and does not enter mucosal cells.
The host's response begins after the bacterium attaches to the epithelial cells, and by damaging the mucosal cells, the antigenic material secreted by the bacterium is absorbed by the gastric epithelial cells and, after passing through the lamina propria (submucosal layer),
It stimulates lymphocytes, resulting in antibodies against the bacteria in the IgG, IgA, and rarely in the IgM class.
After complete treatment, the antibody titer gradually decreases. Note that primary H. pylori infection does not cause immunity and is more likely to be reinfection.
Diagnosis methods
Helicobacter pylori infection is diagnosed using the following methods:
1- Invasive methods
A: Endoscopic biopsy of the gastric mucosa and rapid bioresy test (Biopsy Urease Test): The first choice is a gastric biopsy of the gastric antennae, in which the biopsied sample is placed in a solution containing urea.
Changing the color of the environment is a sign of urea decomposition by H.pylori and alkalization of the environment.
The sensitivity of this method is 100-79% and its feature is 100-92%. Removing a large number of samples, especially from the stomach trunk (in addition to the antrum area), increases the sensitivity of the test.
False-negative cases can be seen in patients with active bleeding or recent bleeding, those who have received antibiotics or have been treated with antisecretory drugs.
B: Endoscopic biopsy of gastric mucosa and culture: Only in cases of resistance to treatment to check its sensitivity to antibiotics and usually not for initial diagnosis of infection, but it is recommended in cases where treatment of the first line with failure confront with,
be done. The bacterium grows at 37 ، C in a microaerophilic environment for 3 to 6 days on a skirrow medium (containing vancomycin, polymyxin B, trimethoprim) or agar chocolate containing vancomycin antibiotics, nalidixic acid, and amphotericin.
2- Non-invasive methods
A: Serological tests:
The methods are inexpensive, but because H. pylori strains vary from region to region, the lack of local antigen in each laboratory diagnostic kit reduces the sensitivity of these tests.
IgG antibodies in 95-94% of patients become positive about 2 months after the bacteria enter the body and remain positive for up to a year or more after the infection has been eradicated.
The specificity of this test is about 41-71%, which is a sign of the above cases of false positives, due to the antibody created in other infections and the creation of a cross-reaction with this test.
IgA class antibodies are positive in 97-94% of patients, approximately 2 months after the arrival of the bacterium in the body, and decrease approximately 3 to 4 weeks after the eradication of the infection.
It has a specificity of about 72-59%, which is a sign of the above positive cases of false positive due to antibodies caused by other infections and cross-reactivity with this test.
IgM antibodies are an insensitive indicator of acute infection (with a sensitivity of about 14-28%) and have no clinical application even in children.
The level of these antibodies has nothing to do with the severity of the infection. On the other hand, these tests are not able to differentiate the active form of the disease from the improved ones.
Serological tests have been used in children to determine treatment protocols, confirm the outcome of definitive treatment, and diagnose the disease in a limited way and are unreliable. On the other hand, early treatment with antimicrobial drugs in H. pylori infection inhibits the response of antibodies, and such patients are prone to re-infection.
B: Urea Breath Test:
This procedure is based on the activity of the enzyme urease, Helicobacter pylori. The urea (14C- or 13C-urea) in the oral capsule eaten by the patient is metabolized to ammonia and CO2 containing carbon, and CO2 is released into the bloodstream through the mucosa, from there to the lungs and eventually It is transmitted to the exhale.
The amount of CO2 produced in the stomach can be measured by collecting the CO2 of the marker in the exhale. If CO2 is detected, it is a sign of an active Helicobacter pylori infection. Due to the very low dose of the drug used in this test, its use is allowed in cases of pregnancy as well as children.
The sensitivity and specificity of this method, which is more than 94% (its positive predictive value or Positive Predictive Value is 100-89% and its negative predictive value or Negative Predictive Value is 94-89%) for the initial diagnosis of infection and follow-up of eradication treatment success User is used.
For this purpose, the test should be repeated at least 4 weeks after the end of the treatment period. Therefore, the reference method (Gold Standard) is to follow the treatment.
This method is also used to diagnose H.pylori in bleeding or non-bleeding peptic ulcers whose Biopsy Urease Test is negative, gastric adenocarcinoma, MALT lymphoma, and a positive family history for gastric cancer.
A: PCR-specific Helicobacter pylori antigen determination test
This test is 89-89% sensitive and has more than 90% feature of the alternative way for urea breath test.
Fecal tests can be performed to ensure effective treatment and should be used 8 weeks after the end of the treatment period. But it is much more expensive than other tests.
How to prepare the patient for the UBT test
The following conditions must be met to perform the test:
1- The patient should be fasting from 6 hours before
2 - Do not take antibiotics, bismuth and antisecretory drugs (such as omeprazole, etc.) 4 weeks before the test
3 - Do not use a variety of antacids and H2 blockers (such as cimetidine, ranitidine, etc.) 7 days before the test
treatment
The goal of H. pylori infection is to completely eliminate the organism. When the bacteria is removed, the chance of re-infection decreases. There are several treatment regimens that include:
Triple therapies:
It includes an antacid (reducing gastric acidity allows the repair of damaged tissues from infection) and 2 antimicrobial agents (two antibiotics are used to reduce the risk of incomplete treatment and drug resistance) for a 7 to 3 course of treatment. It is 14 days.
1- Proton Pump Inhibitors: Proton pump inhibitors directly inhibit H. pylori and appear to be potent urease inhibitors.
Such as: 1- Omeprazole, omeprazole (20 mg, twice daily), 2- Lansoprazol, lansoprazole (30 mg, twice daily), 3- Pantoprazol pantoprazole (40 mg, twice daily), 4 - Raboprazol and 5- Esomeprazol
2- Antibiotics:
A: Metronidazole (500 mg, twice daily) or amoxicillin (1 g, twice daily)
B: clarithromycin (500 mg, twice daily) or tetracycline (500 mg, four times daily)
Four Bismuth-Based Therapy Diets:
In addition to the above diet, bismuth (525 mg sub-salicylate bismuth or bismuth sub-citrate, four times a day) is added. This medication regimen is sufficient for 7 days.
12-5% of H. pylori treatments in the first period lead to failure, in which case re-treatment should be used and another combination of treatments (especially 4-drug regimens based on bismuth) should be used, and the course of treatment is definitely 14 Be the day.
The UBT test is performed 4 weeks after the end of the treatment regimen to ensure that the bacteria are eradicated from the body, which should be ruled out following effective treatment.
Reference:
1- Marshal BJ, and et al. Gasteroentrology, 2008; 99: 697-702.
2- Chen TS, and et al. Clin Diagn Lab Immuno, 2002 Sep; 9 (5): 1044-8
