see also:

• food poisoning
• diarrhoea
• The child with gastroenteritis
• traveller's diarrhoea
• dehydration
• anti-emetics
• the patient with acute abdominal pain in the ED

• the diagnosis of gastroenteritis in the ED is essentially one of exclusion and generally requires both vomiting and diarrhoeal illness.
• in Australia, it is the treating doctor's legal responsibility to notify the government of 2 or more cases of suspected food or water-borne diseases, this is particularly important when those cases arise in Residential Aged Care Facilities
  • see Vic. DHS notification of notifiable infectious diseases
• in general, children should NOT be given anti-emetics (although ondansetron wafers may be considered but may increase amount of diarrhoea) nor anti-diarrhoeal (antimotility) agents - see The child with gastroenteritis
• most cases do NOT need antibiotic Rx, even if they are bacterial.
• increasingly, antibiotic-related Clostridium difficile enteritis is becoming a major problem and can be life threatening.
• gastroenteritis can reduce the absorption of some medications, and patients should be warned of a potential decrease in efficacy (eg the combined oral contraceptive pill)
• some medications are more likely to cause adverse effects if the patient is dehydrated or not eating (eg non-steroidal anti-inflammatory drugs (NSAIDs), ACE inhibitors, angiotensin II receptor blockers, diuretics, digoxin, warfarin, metformin, lithium carbonate).

• gastroenteritis
  • viral
  • bacterial
• colitis
  • C. Diff
  • inflammatory bowel disease (IBD)
  • radiation
  • etc
• pelvic appendicitis
• faecal impaction with overflow incontinence
• diverticulitis
• intussusception
• GIT intolerances eg. acute post-gastro lactose intolerance in infants
• necrotizing enterocolitis of newborn
• other causes of enteritis such as radiation, gonococcal,
• graft vs host disease (dermatitis, hepatitis and enteritis)
• drug induced
• hyperthyroidism or thyroid storm (rare)
• persistent diarrhoea:
  • giardiasis - if symptomatic, Rx with stat tinidazole orally, or a course of metronidazole
  • amoebiasis, schistosomiasis, strongyloidiasis, etc if overseas travel
  • coeliac disease
  • rectal tumours
  • malabsorption syndromes eg. lactose intolerance
  • irritable bowel syndrome
  • short bowel syndrome

• infant
• frail elderly
• 3rd trimester pregnancy
• have prosthetic vascular grafts
• immunocompromised
• achlorhydric
• severe or prolonged illness
• severe invasive disease
• traveller's diarrhoea with presumed shigella/Salmonella typhi (typhoid enteric fever)/paratyphoid enteric fever/cholera
• presumed Clostridium difficile enteritis in which case metronidazole or vancomycin are options.

• viral gastroenteritis
• Salmonella without an indication as generally prolongs carrier status
• enterohaemorrhagic E.coli infections as increases risk of potentially fatal haemolytic uraemic syndrome (HUS)

• loperamide
  • 4 mg orally, for the first dose, then 2 mg orally, after each unformed stool, up to 16 mg per day
• diphenoxylate+atropine
  • 5+0.05 mg orally, 3 to 4 times daily initially, reducing dose as soon as symptoms improve

• viral gastroeneteritis is the most common cause of infectious gastroenteritis in developed countries
• the 4 main viruses are:
  • rotavirus
    • the most common enteric infection in young children
    • most children have been infected with rotavirus by the age of 5 years
    • incubation period 1 to 3 days, followed by vomiting and fever for 1 to 3 days and diarrhoea for 4 to 5 days
    • oral rotavirus vaccine is part of the routine Australian immunisation schedule for infants and has an estimated efficacy of 70%.
  • norovirus
    • probably the commonest cause of gastroenteritis in adults and older children - 18% of all cases worldwide
    • sudden onset of severe projectile vomiting is characteristic of this infection
    • incubation period 1 to 2 days with initial vomiting then diarrhoea for 2-3 days
    • outbreaks in cruise ships, nursing homes and other institutional settings are common and typically occur in winter months
  • adenovirus
    • acute gastroenteritis is usually caused by serotypes 40 and 41, and mainly affects infants and young children
  • astrovirus
    • similar to rotaviral infection but less severe
    • mainly affects day care and school children
    • incubation period 3-4 days
• additionally, in the immunocompromised, reactivation of cytomegalovirus (CMV) can cause serious gastroenteritis

• Campylobacter, Salmonella and E. coli are the most common causes of bacterial enteritis in developed countries and generally do not require antibiotic Rx
  • Campylobacter infections may require antibiotic Rx if severe or prolonged illness, or in immunocompromised, infants, elderly, or perhaps 3rd trimester pregnancy.
  • antibiotic Rx of Salmonella enteritis is not generally advisable as it is usually not clinically beneficial and it may prolong excretion of pathogenic organisms, however, antibiotic Rx is indicated in infants and in patients who are severely ill (eg requiring hospital admission), septicaemic or have prosthetic vascular grafts
    • severe disease from Salmonella is more likely to occur in infants who are malnourished or less than 3 months old, or people who are immunosuppressed, achlorhydric or elderly.
• rarely, outbreaks of enterohaemorrhagic E.coli infections occur which may cause haemolytic uraemic syndrome (HUS) or thrombotic thrombocytopenic purpura (TTP), particularly in children. Do NOT give antibiotics to these patients as it seems to increase the release of Shiga toxins, and thus increases the risk of haemolytic uraemic syndrome (HUS)
• Clostridium difficile is the most important bacterial cause of healthcare-associated enteritis
• Yersinia enterocolitica causes a spectrum of disease including acute enterocolitis, mesenteric adenitis and pharyngitis with or without diarrhoea. Postinfectious complications such as reactive arthritis and erythema nodosum may occur. Antibiotics generally not indicated unless immunocompromised or persistent or extra-intestinal disease.
• overseas travellers are potentially at risk of the following:
  • shigellosis
    • Rx with 5 day course of oral ciprofloxacin or co-trimoxazole
  • typhoid and paratyphoid fevers
    • ideally need sensitivities performed as increasing resistance to flouroquinolone antibiotics
    • if fever for > 7 days or wish to start iv Rx anyway, Rx with iv ceftriaxone, otherwise Rx with azithromycin (or perhaps ciprofloxacin if not contracted from SE Asia).
    • some patients with enteric fever become long-term carriers—seek expert advice.
  • cholera (Vibria cholerae)
    • rarely seen in Australia
    • Rx single dose azithromycin or ciprofloxacin
  • Vibrio parahaemolyticus and other non-cholera Vibrio infections
    • usually from eating shellfish
    • can Rx as for Shigella
  • giardiasis