Acute gastroenteritis in adults

Opening Vignette

Jenny, a 41-year-old administrator, presents to your clinic with nonbloody watery diarrhoea and abdominal cramps of 2 days’ duration. She has just returned from a holiday in Batam yesterday. She has no chronic diseases or previous surgical history and is not on any new medications. There is no fever, nausea or vomiting, and she is still able to tolerate orally. She has no distressing symptoms and is able to carry out her planned activities.

WHAT IS ACUTE GASTROENTERITIS?

Gastroenteritis is inflammation of the stomach, small intestine or large intestine, leading to a combination of abdominal pain, cramping, nausea, vomiting and diarrhoea. It is more known colloquially as ‘food poisoning’, which is gastroenteritis resulting from the ingestion of contaminated food or water. Acute gastroenteritis lasts for less than 14 days.

HOW RELEVANT IS THIS TO MY PRACTICE?

Acute gastroenteritis is one of the most common conditions seen among adult patients in outpatient clinics. As most episodes are benign and self-limiting, general practitioners often discharge patients with rest, return advice and a simple selection of ‘cocktail drugs’ out of the vast inventory of symptomatic medications available.

Because acute gastroenteritis is perceived as a seemingly benign and easy-to-treat condition, general practitioners may not be aware of some of the common pitfalls of management. These include: (a) missing a surgical abdomen or severe illness in the initial evaluation of symptoms; (a) neglecting the importance of general hydration and dietary advice; (c) prescribing errors arising from a lack of understanding of the mechanisms of symptomatic medications, e.g., co-prescription of prokinetic drugs with antimotility drugs; and (d) the inappropriate usage of antibiotics.

We aim to address the aforementioned pitfalls in our approach to evaluation and management of acute gastroenteritis in the ambulatory setting.

INITIAL EVALUATION OF ACUTE GASTROENTERITIS

The diagnosis of acute gastroenteritis is made by a characteristic history of acute diarrhoea, which may be accompanied by nausea, vomiting, fever or abdominal pain. Initial history and physical examination focus on identifying patients with red flag features that warrant further evaluation and hospitalisation [Figure 1]. These include severe dehydration, and symptoms and signs of a surgical abdomen, such as abdominal tenderness with rebound and guarding, abdominal distension, tachycardia and hypotension. High-risk host features include the elderly, pregnant patients, and patients at increased risk of hypovolaemia such as those with cardiac disease or immunocompromised states (e.g., poorly controlled diabetes mellitus, chronic immunosuppression therapy, end-stage kidney disease, untreated or advanced HIV infection). If no red flags are identified, further clues that may suggest other aetiologies may be elicited from the patient’s history and physical examination.

Figure 1.

Chart shows an approach to the evaluation of a patient presenting with acute gastroenteritis symptoms.

Viral gastroenteritis, which is the most common cause of acute gastroenteritis, generally has an intermediate incubation period (24–48 h), a short infection duration (12–60 h) and a high frequency of vomiting. It does not typically cause bloody diarrhoea.

Bacterial causes of acute gastroenteritis are more likely in cases of bloody, mucoid stools, high-frequency diarrhoea, fever and a protracted symptom duration [Figure 1]. There is usually a history of ingestion of contaminated products, and contact or travel history. Travellers’ diarrhoea should be considered if diarrhoea develops within 10 days of returning home from a developing country, since bacterial pathogens account for up to 80%–90% of cases,[1] with Campylobacter species being the most common cause (approximately 30%)[2] in Southeast Asia. The incubation period is typically 4–14 days following arrival in a developing country, and symptoms generally resolve within 1–5 days.

Ingestion of a preformed toxin, such as Staphylococcus aureus enterotoxin or Bacillus cereus emetic toxin, usually presents with a sudden onset of nausea and vomiting as the predominant symptom. Pathogens such as enterotoxigenic Escherichia coli, Clostridium perfringens and Vibrio cholerae, which produce a toxin after consumption, present with watery diarrhoea. Vibrio cholerae is known to cause rapidly dehydrating and profuse watery diarrhoea. In the case of diarrhoea caused by pathogens that directly invade the intestinal wall, such as Campylobacter jejuni or Shigella spp, symptoms may progress to colitis, bloody diarrhoea, tenesmus and fever.

In patients presenting with repeated episodes of self-limiting or acute diarrhoea, noninfectious aetiologies of diarrhoea [Box 1] — such as medications — are often missed but should be evaluated for. In patients with relevant risk factors such as age above 65 years, recent hospitalisation and recent antibiotic use, it is important to consider Clostridium difficile infection, which would prompt further diagnostic testing and contact precaution.

Box 1.

Non-infectious causes of acute gastroenteritis

Medication
• Antibiotics
• Laxative abuse
• Sorbitol
• Colchicine
• Cardiac antiarrhythmic agents
• Nonsteroidal anti-inflammatory drugs
• Hypoglycemic agents (e.g., metformin, gliptins)
• Chemotherapeutic agents
• Antacids
Acute abdominal process
• Mesenteric ischaemia
Gastroenterological diseases
• Irritable bowel syndrome
• Inflammatory bowel disease
• Bile acid diarrhoea
• Malabsorptive disease
• Malignancy
• Celiac disease
• Overflow diarrhoea
• Chronic pancreatitis
• Radiation enteropathy
• Small bowel bacteria overgrowth
• Cystic fibrosis
• Other small bowel enteropathies (e.g., Whipple’s disease, tropical sprue)
Endocrine diseases
• Hyperthyroidism
• Hypoparathyroidism
• Addison’s disease
• Diabetes mellitus
• Hormone secreting tumours (gastrinoma, carcinoid, vasoactive Intestinal Peptide-secreting tumour)
Toxic ingestion
• Organophosphates
• Arsenic

Stool studies in the form of stool cultures or multiplex molecular panel tests are not routinely recommended due to low diagnostic yield, since most cases of acute gastroenteritis are viral and self-limiting.[3] In a study of 13,327 patients who underwent stool cultures due to diarrhoeal illness, only 1.47% were diagnosed with positive stool culture, with clinical features such as fever (odds ratio [OR] 2.33, 95% confidence interval [CI] 1.25–4.35, P = 0.008) and frequency of diarrhoea (OR 3.52, 95% CI 1.93–6.44, P < 0.001) being independent predictors of a positive stool culture.[4]

Stool studies are thus reserved for high-risk patients or those with severe illness, for whom identification of a bacterial pathogen may inform treatment decisions or the potential for complications. For the majority of patients, expectant management may be continued without determination of the microbiological agent.

NONPHARMACOLOGICAL MANAGEMENT

Rehydration is the cornerstone of management of acute gastroenteritis. An oral rehydration solution (ORS) must contain a mixture of salt and glucose in water to best utilise the intestine’s sodium–glucose coupled cellular transport mechanism. In mild illness, most individuals can replenish fluids and salt by consuming liquids such as diluted juices, sports drinks, soups and saltine crackers.[5] Soft drinks and fruit juices that are high in sugar content should be avoided, as they may cause osmotic diarrhoea. In more severe illness, ORS is recommended.[6]

Although dietary or solid food restriction is commonly recommended, evidence for it is limited.[7] Smaller meals, bland and low-residue foods like broiled starches or cereals may be better tolerated than other food. Milk and dairy products may be excluded during an episode of acute gastroenteritis, although evidence supporting their exclusion is weak.[8]

ANTIBIOTIC THERAPY

Routine antibiotic use is not recommended since acute gastroenteritis is usually self-limiting and caused by virus. However, it may be appropriate in cases of bacterial gastroenteritis with severe symptoms (protracted duration of more than a week, severe dehydration) and some cases of travellers’ diarrhoea.[9]

For travellers’ diarrhoea, antibiotics have been shown to reduce the severity and duration of illness by 2–3 days.[10] However, this benefit must be weighed against the adverse consequences of antibiotics use. These include disruption of normal gastrointestinal flora, acquisition of resistant organisms such as extended-spectrum β-lactamase-producing organisms and their subsequent introduction into the community, increased costs, and allergic or adverse reactions. For these reasons, prophylactic antibiotics are currently not recommended.[11]

To guide antibiotic use in travellers’ diarrhoea, the Centers for Disease Control and Prevention (CDC) has published a set of guidelines [Box 2].[1] Travellers’ diarrhoea is classified as mild (symptoms are not distressing and do not interfere with planned activities), moderate (symptoms are distressing and interfere with planned activities) and severe (bloody diarrhoea, or symptoms that are incapacitating and completely prevent planned activities). Based on CDC guidelines, antibiotics are recommended in severe illness, may be considered in moderate illness, and should not be recommended in mild cases.

Box 2.

Treatment recommendations for travellers’ diarrhoea. (Adapted from Centers for Disease Control and Prevention Yellow Book 2020)[1]

Mild travellers’ diarrhoea
• Antibiotic treatment is not recommended
• Loperamide or bismuth subsalicylate may be considered
Moderate travellers’ diarrhoea
• Antibiotics may be used
• Fluoroquinolones may be used
• Azithromycin may be used
• Loperamide may be used as adjunctive therapy for moderate to severe travellers’ diarrhoea. Antimotility agents alone are not recommended for patients with bloody diarrhoea or those with diarrhoea and fever
• Loperamide may be considered for use as monotherapy
• Rifaximin may be used to treat moderate, non-invasive travellers’ diarrhoeaa
Severe travellers’ diarrhoea
• Antibiotics should be used
• Azithromycin is preferred
• Fluoroquinolones may be used to treat severe, non-dysenteric (non-bloody) travellers’ diarrhoea • Single-dose antibiotic regimens may be used
• Rifaximin or rifamycin SV may be used to treat severe, non-dysenteric travellers’ diarrhoeaa

^aRifaximin and rifamycin SV are currently not licensed for use in Singapore for this indication.

The recommended antibiotic regimens are presented in Table 1. First-line antibiotics have traditionally been fluroquinolones such as ciprofloxacin and levofloxacin. However, due to increasing fluoroquinolone resistance, particularly in C. jejuni isolates in South Asia and Southeast Asia, azithromycin is the preferred treatment for dysentery (bloody diarrhoea) or febrile diarrhoea in travellers with relevant exposures.

Table 1.

Antibiotic treatment recommendations. (Adapted from Centers for Disease Control and Prevention Yellow Book 2020)[1]

Antibiotic	Dose	Duration
Azithromycina	1000 mg	Single or divided doseb
	500 mg daily	3 days
Levofloxacin	500 mg daily	1–3 daysb
Ciprofloxacin	750 mg	Single doseb
	500 mg twice daily	3 days
Ofloxacin	400 mg twice daily	1–3 daysb

^aAzithromycin is the preferred regimen for dysentery or febrile diarrhoea.^bIf symptoms are not resolved after 24 h, continue daily dosing for up to 3 days.

OTHER PHARMACOLOGICAL MANAGEMENT

Antiemetic agents

Antiemetic agents may be used to decrease nausea and vomiting in gastroenteritis, so as to facilitate oral fluid repletion. Although studies in adult populations are limited, ondansetron (5-hydroxytryptamine (5-HT3) receptor antagonist) is one of the best-studied antiemetics in the paediatric population, with proven efficacy in enhancing compliance of oral rehydration therapy and reducing hospitalisation rates.[12] Antiemetics such as diphenhydramine (antihistamines) or ondansetron may be prescribed for 1–2 days. Phenothiazines such as prochlorperazine (dopamine 2 receptor antagonist) are used for patients who remain symptomatic despite treatment with antihistamines and 5-HT3 antagonists due to prolongation of QT interval and central side effects.

Antimotility agents

Antimotility agents are indicated to decrease stool output. These include loperamide (Imodium), narcotics and diphenoxylate (Lomotil). Of these, loperamide is most commonly used due to its best safety profile and highest efficacy. In travellers’ diarrhoea, it has been shown to reduce duration of illness and improve clinical cure when used in combination with antibiotics.[13] However, for patients with bloody diarrhoea, loperamide should be avoided, as it may cause dangerous prolongation of illness.[14] Diphenoxylate is an alternative antimotility agent, but it has not been as well studied and may cause central opiate or cholinergic side effects. When antimotility agents are employed, patients should be cautioned to use fluids aggressively, as the pooling of fluid in the intestines may mask actual fluid losses.

Antisecretory agents

In patients with fever and bloody diarrhoea, the antisecretory drug, bismuth subsalicylate, is a safe alternative to loperamide, which should be avoided. Bismuth colloids have an antibacterial action, while the salicylate component exerts intestinal anti-inflammatory and antisecretory actions. When compared to placebo, it significantly reduced the number of unformed stools and increased the proportion of patients who were free of symptoms at the end of the treatment trials.[15]

Prokinetics are not indicated for acute gastroenteritis, although they are commonly prescribed for this indication in the ambulatory setting. Instead, they are indicated for patients with gastroparesis, where there is delayed gastric emptying with cardinal symptoms of nausea, vomiting, early satiety, bloating and upper abdominal discomfort. Prokinetics increase the rate of gastric emptying by enhancing gastric contractions and decreasing postprandial fundus relaxation. Commonly prescribed prokinetics include metoclopramide (dopamine 2 receptor antagonist and 5-hydroxytryptamine receptor 4 [5-HT4] agonist) and domperidone (dopamine 2 antagonist).

TAKE HOME MESSAGES

1. Viruses are the most common cause of gastroenteritis.

2. Bacterial gastroenteritis is more likely in the presence of bloody stools, passage of mucous, fever, a protracted duration of symptoms and/or a positive travel history.

3. Antibiotic therapy may be considered in bacterial gastroenteritis with severe symptoms, presence of immunocompromised states, and in moderate or severe travellers’ diarrhoea. The risk of increasing bacterial resistance should be considered when prescribing antibiotics.

4. Identification of microbial aetiology in the form of stool testing is not routinely recommended due to low diagnostic yield.

5. Antiemetic, antimotility and antisecretory agents may be used to manage symptoms in acute gastroenteritis. Prokinetic agents are not routinely recommended.

6. Loperamide improves clinical cure of travellers’ diarrhoea when used with antibiotics, but it should be avoided in inflammatory or bloody diarrhoea.

Closing Vignette

You prescribe 5 days of loperamide for what is likely an episode of viral gastroenteritis and advise Jenny to return if her symptoms do not improve after 3 days. Her symptoms subsequently resolve 2 days later.

Conflicts of interest

How CH is the handling editor of the PILL series.

SMC CATEGORY 3B CME PROGRAMME

Online Quiz: https://www.sma.org.sg/cme-programme

Deadline for submission: 6 pm, 19 September 2025

Question: Answer True or False
1. Viral gastroenteritis is the most common cause of acute gastroenteritis.
2. Viral pathogens are the most common cause of travellers’ diarrhoea.
3. Concern for community outbreaks constitutes a red flag feature that may warrant hospitalisation and further evaluation.
4. Initial history and physical examination should focus on identifying patients with red flag features such as severe dehydration, surgical abdomen and high-risk host features.
5. Bloody diarrhoea is suggestive of viral gastroenteritis.
6. Ingestion of a preformed toxin, such as Staphylococcus aureus enterotoxin or Bacillus cereus toxin, usually presents with profuse watery or bloody diarrhoea.
7. In patients with recent hospitalisation and recent antibiotic usage, it is important to consider Clostridium difficile infection.
8. Stool studies are routinely performed in most cases of acute gastroenteritis to identify causative pathogens.
9. Stool studies are frequently able to identify causative pathogens and guide management.
10. Routine antibiotic use is not recommended in most cases of acute gastroenteritis as most are self-limiting and/or caused by viruses.
11. Rehydration and prevention of dehydration are the cornerstones of outpatient management of acute gastroenteritis.
12. Antiemetic, antimotility and antisecretory agents may be considered in cases of acute gastroenteritis to relieve symptoms and facilitate oral rehydration.
13. Prokinetic agents such as metoclopramide and domperidone are useful in relieving symptoms of acute gastroenteritis.
14. Antibiotics may be appropriate in some cases of acute bacterial gastroenteritis.
15. Travellers’ diarrhoea should be considered if diarrhoea develops within 10 days of returning home from a developing nation.
16. Prophylactic antibiotics against travellers’ diarrhoea are routinely recommended for those travelling to developing nations.
17. The Centers for Disease Control and Prevention recommends considering antibiotics for moderate to severe travellers’ diarrhoea but not for mild travellers’ diarrhoea.
18. Fluoroquinolones and azithromycin are the recommended antibiotics of choice for moderate travellers’ diarrhoea.
19. Bismuth subsalicylate has been shown to significantly reduce symptoms in patients with inflammatory diarrhoea.
20. Loperamide is recommended for bloody diarrhoea, as it reduces the severity and duration of symptoms.

Funding Statement

Nil.