Gastrointesinal Tract Infections And Hepatitis

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Defences against infection

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Enzymes in saliva and small intestine

Acid environment of the stomach

Bile in the small intestines

Mucosa and mucin

Physical movement preventing close approximation with wall of intestines

Secreted IgA and peyer's patches

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Gastroenteritis

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One of the most common infections. Dependent on location, hygiene, food poisoning and other factors. Symptoms: fever, abdominal cramps, diarrhoea, loss of appetite, vomiting and dehydration.

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Viral gastroenteritis

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Spread through faecal-oral spread. Causes explosive diarrhoea often with vomiting and is incredibly infectious with an incubation period of 24-48 hours. Treated with supportive management e.g. rehydration

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E.coli

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Variable presentation from mild diarrhoea to haemolytic uraemic syndrome (8%). Effects are mediated by vero-cytotoxin (shiga toxin) which is very potent. Transmitted between people and from cattle. Incubation period of 2-10 days

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Haemolytic uraemic syndrome (HUS)

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Severe life threatening condition with haemolysis and renal failure that often results in dependence on dialysis in survivors.

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Salmonella

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Most commonly caused by food poisoning (eggs/chicken). Most common subspecies is S. enteritidis which causes self limiting diarrhoea and most severe is S.typhi and S.paratyphi which causes sepsis with possible secondary seeding. Occasionally carrier state occurs especially if infection is in the bladder.

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Shigella

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Subspecies include S.dysenteriae, S.boyoii, S.sonei, S.flexries and most severe is systentry. Highly contagious and spread by faecal-oral contact. Causes haemorrhagic colitis, fluid loss, HUS, toxic megacolon and shock. IP = 1-3 days.

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Campylobacter

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A zoonotic bacterial infection with C.jejuni or C.coli. Causes abdominal pain, malaise, fever, nausea, and vomiting. Acquired from contaminated food (raw chicken) and water. IP = 2-5 days.

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Toxin-mediated food poisoning

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Staphylococcus aureus causes sudden onset abdominal pain and vomiting. Clostridium perfringens causes occasional necrotising enteritis. Bacillus cerus is a spore forming organism: heat stable ones causes vomiting, heat labile one causes diarrhoea. IP = few hours and can be life threatening.

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Parasites

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Giardia lamblia, cryptosporidium parvum and entamoeba histolytica. Waterborne from faecally contaminated water supples. Infection is often travel related. IP = 7-10 days. Cryptosporidium is self-limiting. Giardia and entamoeba are treated with metronidazole. Diagnosed by finding cysts or protozoa in concentrated stool specimens.

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H.pylori

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20-30% population is affected. A gram -ve spiral curved bacillus that is motile, urease +ve, lives in our stomach and requires microaerophilic conditions to grow. Causes chronic gastritis, duodenal ulcers, inflammation, epigastric pain, nausea, vomiting, haematemesis and blood stained stools. Associated with gastric adenocarcinoma. IP=5-10days. Transmission is oral-oral or faecal-oral.

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C.difficile

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Anaerobic gram +ve bacillus that forms endospores. Causes self-limiting diarrhoea, pseudomembranous colitis, toxic megacolon, abdominal cramping and fever. Transmitted via spores. 5% adults and 70% of neonates are carriers. Treated with antibiotics, prebiotics, probiotics, faecal transplants and immunotherapy.

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Hepatitis

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Infection of the liver that causes inflammation. Most commonly viral. Non-viral causes: leptospirosis and brucellosis. Causes abscesses that can be amoebic or pyogenic.

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Feature of acute viral hepatitis

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Preicteric symptoms include malaise, anorexia, nausea, abdominal discomfort and pyrexia (fever). Icteric symptoms include jaundice, pale stools and dark urine.

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Hepatitis A virus

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An enteric virus with an RNA genome with positive single stranded RNA. Transmitted faecal-oral through contaminated food or water and is then excreted in faeces. Asymptomatic is the most likely outcome in young people. Other outcomes are acute icteric hepatitis and fulminant hepatitis. Prevented by taking care with food and water or vaccination.

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Fulminant hepatitis

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Infection of the small bowel wall. It is rare but has fatality of 70% and a liver transplant is required for survival.

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Hepatitis B virus

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Partially double stranded small genome encoding 4 proteins. Modes of transmission include perinatal, sexual and parenteral. Outcomes are subclinical infection, acute icteric hepatitis, fulminant hepatitis or chronic infection. Can be prevented by simple precautions, by immunoglobulin (passive immunisation) and vaccination.

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Chronic hepatitis B infection

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Chronic HBV is defined as persitence of HBsAg for more than 6 months. Chronic infection occurs in 10%. It may resolve itself, lead to chronic hepatitis or lead to cirrhosis due to calcium. It takes 10-20 years for a chronically infected individual to progress from healthy to chronic hepatitis then cirrhosis. Most neonates infected with HBV become chronic carriers.

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Hepatitis E virus

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Similar to hepatitis A but higher mortality rate as it is more pathogenic. Transmission is through faecal-oral spread. No chronic infection. Associated with travel abroad but endogenous infection is increasing recognised.

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Hepatitis C virus

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Blood borne virus. Has large genetic diversity. 1-6 genotypes geographically distributed with greater than 30% differences that don't respond equally to treatment. Results in acute asymptomatic infection or chronic infection (75%). Transmitted by injecting drug use, blood/blood product transfision and inappropriate use of unsterilised needles.

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Chronic hepatitis C infection

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Chronic infection disposes to chronic hepatitis, cirrhosis and hepatocellular carcinoma. Things that cause faster progression include being male, older at age of infection and increased alcohol intake.

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Cholecystitis

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Infection of the gall bladder usually secondary to gall stones. CAuses abdominal pain in the right upper quadrant and back, tenderness, fever and vomiting. Causes by gut organisms e.g. anaerobes, coliforms (E.coli). Diagnosed by symptoms, imaging and stool cultures.

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Cholangitis

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Infection of the biliary tree usually secondary to obstruction e.g. by gall stones or calcified head of the pancreas. Clinically similar to cholecystitis but fever, rigors and jaundice are more prominent. Caused by gut organisms and diagnosed by stool cultures.

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Pancreatitis

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Usually due to gallstones or alcohol but secondary bacterial infection can occur.

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Peritonitis

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Inflammation of the peritoneal cavity that usually arises as a secondary complication to other intra-abdominal pathology with perforation and release of gut organisms into the peritoneum. Often polymicrobial including aerobes such as coliforms or enterococci. It is life threatening.