Gut Infections

a) Toxigenic (shorted incubation periods)

  • Staphylococcus Aureus

This is a Gram-positive bacterium which produces toxins that give inflammation of the intestine

– Infection is due to the toxin not the bacteria which means it has a short incubation period of 1-6 hours

– Bacteria makes enterotoxins to compete with other bacteria in cooked and processed foods, but these end up being ingested by humans causing symptoms


Symptoms – These takes 1-6 hours to develop

– Nausea and explosive vomiting up to 24 hours

– Abdominal pain, weakness and headache


Tests – Stool culture to assess if bacterium is present

Management – Fluid and electrolyte replacement as illness quickly resolves within a couple days


  • Bacillus Cereus

This is a Gram-positive rod bacterium which typically is found in the soil and water

– It usually causes food poisoning but also causes host of infections in immunocompromised patients

– Classically associated with eating under-cooked or reheated rice e.g. from Chinese takeaways


Symptoms – It cause 2 main types of syndromes:


i) Emetic Syndrome –> This is due to ingestion of the toxin cereulide which is stable in high temperatures

                  – This means that it survives the cooking process and can be ingested by humans

                  – Gives vomiting 1-6 hours after ingestion and resolves within 1 day


ii) Diarrhoeal syndrome –> due to toxins like haemolysin which give crampy stomach pain and diarrhoea

                  – Symptoms develop 8-15 hours after ingestion and resolve within 1 day


Management – Usually self-limiting within 24 hours


b) Bacterial (Medium incubation periods)

  • Typhoid

This is an infection due to the bacteria Salmonella typhi, which is spread faeco-orally

– Incidence is highest in children. Geographically, the highest prevalence of the disease is in India.

– The bacteria infect the gut but then enter the blood giving systemic symptoms

Symptoms – Divided in 4 stages each lasting around 1                                                    week

i) Week 1 –> fever with malaise, headache and cough

ii) Week 2 –> High fever (40ºC) + bradycardia

                        – Muscle aches and complete exhaustion

                        – Rose spots seen on lower chest + abdomen

                        – Abdomen becomes distended with                                                              constipation

iii) Week 3 –> Complications e.g. GI bleed, meningitis,

                        – Cholecystitis

                        – Osteomyelitis –> especially in sickle cell                                                     disease

iv) Week 4 –>  Symptoms start to subside

Diagnosis – Cultures grown from blood, bone marrow or stool

– Can also diagnose with the Widal test (serological for Salmonella antigens)


Management – Oral rehydration therapy + ciprofloxacin


  • Cholera

An infection of the small intestine due to gram-negative bacteria Vibrio Cholerae

– It is spread by food and water contaminated by human faeces containing bacteria

– Colonises the small intestine releasing cholera toxin causing cAMP production

– This opens sodium, potassium and HCO3 channels in cells meaning they secrete ions and water which leads to loss of water and rapid dehydration

Symptoms – Start suddenly from 1-5 days after ingestion

– Watery vomiting and high volume watery “rice-water” diarrhoea

– Dehydration –> cold skin, sunken eyes, wrinkling of hands and feet

– Electrolyte imbalance and hypoglycaemia


Diagnosis – Rapid dipstick test available, but stool test is definitive


Management – Oral rehydration therapy + antibiotics (doxycycline) if needed


  • E. Coli

This is a Gram-negative rod which is present in the gut as a commensal bacterium but can cause infection

– It gives neonatal meningitis, urinary tract infections but also types of diarrhoea according to strain

– Sub-classified into specific E.coli species by the antigens that trigger an immune response:

Antigen O = Lipopolysaccharide layer         K = Capsule                 H = flagellin


i) Enterotoxigenic E. Coli –> This type is the main cause of traveller’s diarrhoea spread through food/water

                  – It secretes enterotoxins which leads to watery diarrhoea with cramps and nausea

                  Treatment – Most resolve without treatment so give oral rehydration salts


 ii) Enterohaemorrhagic E. Coli –> this is E. Coli 0157:H7 which is spread by contaminated beef

                  – It produces the Shiga toxin which gives a severe, haemorrhagic bloody diarrhoea

                  – Mortality rate is high and can lead to Haemolytic uraemia syndrome in children.


iii) Uropathogenic E. Coli –> this is one of main causes of urinary tract infections



  • Dysentery

This is a type of gastroenteritis that causes diarrhoea with blood

– It is usually due to the bacteria Shigella which is spread by food contaminated with faeces

– The bacteria colonies the large intestine and makes cytotoxins giving inflammation and bleeding


Symptoms – These take 2-3 days to develop

– Large volume bloody diarrhoea with abdominal pain and a feeling of incomplete defecation

– Fever and dehydration

– Nausea/vomiting is rare


Diagnosis – Stool culture


Management – Oral rehydration therapy + antibiotics (ciprofloxacin) if very severe


  • Campylobacter

This is a Gram-negative bacterium which is usually found in poultry (so enquire about history of chicken)

– The strains C. Jejuni and C. coli are one of the main causes of bacterial gastroenteritis

– Usually transmitted by contaminated food/water e.g.  raw poultry, raw dairy products


Symptoms – These take 2-3 days to develop

– Prodrome of fever + fatigue (flu-like) then abdominal crampy pain and (bloody) diarrhoea

– Can lead to Guillain-Barre syndrome


Diagnosis – Stool tests


Management – Usually self-limiting and symptoms resolve after 5-7 days. Give fluids and electrolytes


c) Parasitic (Longest Incubation Periods)

  • Amoebiasis

This is an infection caused by the parasite Entamoeba histolytica. Transmission is faeco-orally.

– It can be completely asymptomatic but can cause severe dysentery and liver abscesses

– It is transmitted through contaminated food and water and seen more in the developing world


Symptoms – These take 2-4 weeks to develop

– Gives bloody diarrhoea with intense abdominal pains

– Can lead to ulceration of the intestines

– Liver abscess –> parasite enters bloodstream and migrates to liver giving RUQ pain and fever

– Presents as mass in the right lobe, which is filled with pus described as “anchovy sauce”


Diagnosis – Need a “hot stool sample” which shows trophozoites

– Serological tests (these are more sensitive if liver abscess)


Management – Metronidazole



  • Giardiasis

An infection due to the protozoan Giardia lamblia, spread faeco-orally

– It can be completely asymptomatic but can cause chronic diarrhoea

– It is spread when the cysts in faeces contaminate water and food, usually in developing world

Symptoms – These take 1-2 weeks to develop and last up to 6 weeks

– Lethargy

– Abdominal pain and bloating

– Chronic non-bloody diarrhoea which is foul smelling and floats

– Malabsorption of nutrients –> gives fatty stool, weight loss and fatigue


Diagnosis – Stool sample to look for trophozoites


Management – Metronidazole


 d) Viral

  • Norovirus

Norovirus is the commonest cause of gastroenteritis. Sometimes referred to as the “winter vomiting bug.”

– Virus is spread by faeco-oral route which can be in contaminated food/water but also person-to-person

– Commonly spreads in environments where people kept in close contact e.g. hospitals

– No vaccine exists, and alcohol hand-sanitizer is non-effective so can only prevent it by washing hands

– Transmission can be aerosolized e.g. Vomiting in toilet spreads particles in air that others breathe in


Symptoms – These develop 12-48 hours after exposure

– Nausea, vomiting and watery diarrhoea

– Abdominal pain and lethargy

– Weakness and low-grade fever


DiagnosisStool culture PCR


Management – Disease is usually self-limiting but manage symptoms with fluids and antiemetics


1. CDC/Armed Forces Institute of Pathology, Charles N. Farmer / Public domain
2. CDC / Jessica A. Allen, Illustrator: Alissa Eckert, MS / Public domain

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