Describe Helicobacter pylori with its pathogenesis, associated diseases and diagnosis.

The Organism

• A gram-negative, curved or S-shaped (spiral) bacillus with multiple sheathed polar flagella giving rapid corkscrew motility through mucus
• Microaerophilic; slow-growing and fastidious
• Strongly urease positive — the central property, and the basis of both its survival and almost every test used to detect it
• Also oxidase and catalase positive
• Colonises the gastric antrum, living in the mucus layer adjacent to the epithelium rather than invading it
• Prevalence exceeds 70% in India, acquired in childhood by the faecal-oral or oral-oral route, and associated with crowding and poor sanitation
• Urease splits urea into ammonia and carbon dioxide → Ammonia neutralises gastric acid in the immediate surroundings → The organism survives the most hostile environment in the body and burrows through mucus using its flagella → It adheres to gastric epithelium
• CagA and VacA are injected or secreted, causing cell injury → Chronic active gastritis → Depending on the pattern — antral gastritis raises acid and causes duodenal ulcer
• body-predominant gastritis causes atrophy, reduces acid and predisposes to gastric ulcer and carcinoma

Associated Diseases

• Chronic gastritis — in essentially all colonised individuals, though most remain asymptomatic
• Peptic ulcer — associated with over 90% of duodenal ulcers and about 70% of gastric ulcers; eradication cures the ulcer disease and prevents recurrence, which transformed a chronic relapsing surgical condition into a curable infection
• Gastric adenocarcinoma — classified by the WHO as a group 1 carcinogen; the sequence runs chronic gastritis, atrophy, intestinal metaplasia, dysplasia, carcinoma
• Gastric malt lymphoma — remarkably, low-grade disease frequently regresses with eradication alone, without chemotherapy; a unique example of an antibiotic curing a malignancy
• Other associations — unexplained iron deficiency anaemia and immune thrombocytopenia, in which eradication is recommended

Diagnosis

• Proton pump inhibitors, antibiotics and bismuth cause false negatives and must be stopped — antibiotics and bismuth for 4 weeks, and proton pump inhibitors for 2 weeks — before breath, stool, urease or histological testing

Treatment and Applied Aspects

• Standard triple therapy — a proton pump inhibitor with clarithromycin and amoxicillin (or metronidazole) for 14 days
• Quadruple therapy — proton pump inhibitor, bismuth, tetracycline and metronidazole, used where clarithromycin resistance is high, which now includes much of India
• Acid suppression is part of the treatment, not merely symptomatic: the antibiotics work far better at a higher gastric pH
• Confirm eradication at least 4 weeks after treatment by urea breath test or stool antigen — never by serology
• Resistance is rising rapidly in India, particularly to clarithromycin and metronidazole, largely from their widespread use for other indications; this is shifting practice towards quadruple and sequential regimens
• Do not test and treat indiscriminately; test those with peptic ulcer, malt lymphoma, a family history of gastric cancer, unexplained iron deficiency, or requiring long-term NSAIDs — eradicating in every dyspeptic patient drives resistance without proportionate benefit