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Infectious Diseases and Microbiology: Diarrhea and Fever
Basics
Description
Diarrhea is defined as stool output exceeding 200 g/day and, in practice, as three or more loose stools daily. It is acute when <14 days and chronic when>4 weeks. Inflammatory diarrhea presents with frequent, small-volume stools that are mucoid and/or bloody and may include tenesmus, fever, or severe abdominal pain; stool leukocytes are a key feature. Noninflammatory diarrhea is typically watery, may be high volume (>1 L/day), and occurs without blood, pus, severe pain, or fever.
Epidemiology
Incidence
In the United States, acute diarrhea occurs hundreds of millions of times yearly, with tens of millions of episodes linked to identified pathogens, and foodborne spread accounting for a large proportion of known-pathogen disease. Surveillance data have identified non-typhoidal Salmonella, Campylobacter, Shigella, Cryptosporidium, and Shiga toxin–producing E. coli O157 as leading reported causes, with highest bacterial diarrhea rates from Salmonella, Campylobacter, and Yersinia in infants under one year. Post-diarrheal hemolytic uremic syndrome occurs infrequently overall but is most common in children under five. Traveler’s diarrhea affects a substantial fraction of international travelers.
Risk Factors
Risks include consuming undercooked eggs, meat, poultry, seafood, or unpasteurized dairy, and drinking untreated surface water. Greater severity or pathogen-specific risk occurs with HIV, immunosuppressive therapies (including glucocorticoids, TNF inhibitors, and chemotherapy), recent antibiotic exposure, liver disease, neutropenia, malnutrition, zinc deficiency, and IgA deficiency. Oral–anal sexual contact increases risk of enteric infection. Antibiotic exposure is a major risk factor for Clostridioides difficile–associated diarrhea.
General Prevention
Handwashing before eating or food preparation, avoiding undercooked animal products and unpasteurized dairy, and avoiding untreated stream or river water reduce risk. During travel in areas with unsafe water, avoid tap water and ice. Typhoid vaccination is available for travelers, and infant rotavirus vaccination is recommended in the United States; destination-based vaccine guidance is available through travel medicine resources.
Etiology
Bacterial causes include Campylobacter, Salmonella, Shigella, Yersinia enterocolitica, C. difficile, Vibrio cholerae, Vibrio parahaemolyticus, Aeromonas, Plesiomonas shigelloides, and multiple diarrheagenic E. coli pathotypes including ETEC, EPEC, EIEC, STEC (including O157:H7), and EAEC. Viral causes include rotavirus, human caliciviruses such as norovirus, adenovirus, and cytomegalovirus. Parasitic causes include Giardia intestinalis, Cryptosporidium parvum, Entamoeba histolytica, Cyclospora cayetanensis, Isospora belli, and Strongyloides stercoralis. Toxin-mediated syndromes include Staphylococcus aureus, Bacillus cereus, and Clostridium perfringens.
Diagnosis
History
Evaluation should define likely cause, illness severity, and complications. Ask about travel, diet, antibiotic use, sexual practices, day-care exposure, sick contacts, outbreaks, seasonality, and other illnesses, and characterize stool frequency, duration, and appearance. Infectious diarrhea may include fever, chills, vomiting, nausea, abdominal pain, and tenesmus. Dizziness, presyncope, or syncope suggests volume depletion. Dysentery points to invasive pathogens such as Shigella, Salmonella, Campylobacter, STEC (often without fever), or Yersinia. STEC commonly starts watery and becomes bloody and is frequently associated with contaminated beef or produce; fever is often absent. Yersinia and Salmonella may involve the terminal ileum and cecum, producing right lower quadrant pain that mimics appendicitis. Watery diarrhea alone is nonspecific. Enterotoxin-mediated food poisoning from S. aureus, B. cereus, or C. perfringens typically has a short incubation and brief course, with vomiting alone more typical of S. aureus or C. perfringens and watery diarrhea more typical of B. cereus or C. perfringens; fever is usually absent. Extraintestinal features such as arthritis, skin lesions, or eye symptoms suggest inflammatory bowel disease. With recent international travel, likely pathogens depend on location, setting, and season, commonly including ETEC, EAEC, Campylobacter, Salmonella, and norovirus, and travel medicine resources can guide evaluation.
Physical Examination
Assess blood pressure, heart rate, respiratory rate, temperature, and mental status to gauge severity. Look for dehydration signs such as dry mucous membranes, reduced skin turgor, sunken eyes, delayed capillary refill, low jugular venous pressure, and orthostatic hypotension. Examine for abdominal tenderness, peritoneal signs, hepatomegaly, and splenomegaly.
Diagnostic Tests and Interpretation
Laboratory Studies
Testing is indicated with fever, systemic toxicity, bloody stools, dehydration, suspected foodborne outbreak, recent international travel, immunosuppression, or recent antibiotic exposure. Send stool for culture, noting that routine processing commonly targets Shigella, Salmonella, and Campylobacter, so the laboratory should be alerted if suspicion is high for STEC or other E. coli pathotypes, Yersinia, Vibrio, or other organisms. Stool culture yield is generally low. For bloody diarrhea, culture for Salmonella, Shigella, Campylobacter, and STEC and obtain a Shiga toxin immunoassay; if E. coli is isolated, arrange serotyping via a reference laboratory. If there is recent antibiotic exposure, recent hospitalization, day-care exposure, or recent chemotherapy, test stool for C. difficile toxins. If diarrhea persists beyond seven days, submit multiple stools for ova and parasite examination with attention to Giardia, Cryptosporidium, Isospora, and Cyclospora and consider noninfectious causes; in AIDS or immunosuppression, also evaluate for microsporidia, Mycobacterium avium complex, and cytomegalovirus. Fecal polymorphonuclear cells support an inflammatory process. If dehydration or severe illness is present, obtain electrolytes, renal and liver function tests, complete blood count, and blood cultures.
Imaging
If the diagnosis remains unclear in critical illness, with prominent abdominal pain or peritoneal signs, consider CT abdomen with oral and intravenous contrast.
t
Diagnostic Procedures/Other
Further evaluation may require upper endoscopy or colonoscopy with biopsies
.
Differential Diagnosis
Acute inflammatory diarrhea may be noninfectious, including ulcerative colitis, Crohn disease, radiation or ischemic colitis, partial obstruction, diverticulitis, laxative abuse, rectosigmoid abscess, Whipple disease, pernicious anemia, diabetes-related enteropathy, malabsorption disorders, scleroderma, or celiac disease. Fever and diarrhea can also result from infections outside the gut such as malaria or sepsis.
Treatment
Medications
Core management is rehydration with selective antibiotic use. Oral rehydration is effective and cost-efficient across settings, while intravenous fluids are indicated for severe dehydration or major electrolyte disturbances; rice-based oral solutions are superior for cholera in children and adults. Antibiotics are recommended for severe infection and for persistent gastroenteritis and are favored in adults over 65, immunocompromised patients, those with prosthetic material, and invasive infections, except when STEC is suspected or confirmed. Empiric therapy for febrile community-acquired invasive diarrhea or moderate to severe traveler’s diarrhea includes ciprofloxacin 500 mg twice daily or levofloxacin 500 mg daily while awaiting studies unless STEC is suspected; travel to Southeast Asia raises concern for fluoroquinolone-resistant Campylobacter. For suspected antibiotic-associated or nosocomial diarrhea, treat empirically with metronidazole or vancomycin while awaiting C. difficile testing. Pathogen-directed therapy includes treating non-typhoidal Salmonella in high-risk or severe disease with fluoroquinolones, TMP-SMX, or ceftriaxone for typical short courses and longer courses in immunocompromised patients, recognizing antibiotics may prolong shedding; treating Shigella with short-course fluoroquinolones or TMP-SMX when susceptible and longer courses for severe or immunocompromised cases; treating Campylobacter with erythromycin while acknowledging high fluoroquinolone resistance especially in Southeast Asia; avoiding antibiotics in STEC due to increased HUS risk and providing supportive care; treating ETEC/EPEC/EIEC similarly to traveler’s diarrhea regimens; usually avoiding antibiotics in Yersinia unless severe or immunocompromised, in which case doxycycline plus an aminoglycoside, fluoroquinolones, or TMP-SMX may be used; managing C. difficile by stopping unnecessary antibiotics and using metronidazole for milder disease or oral vancomycin for 10–14 days; prioritizing fluids in cholera with antibiotics guided by local resistance; treating amebiasis with metronidazole followed by a luminal agent such as paromomycin or iodoquinol; treating giardiasis with metronidazole or single-dose tinidazole; and treating Cyclospora or Isospora with TMP-SMX with extended therapy and possible suppression in immunocompromised hosts.
Additional Treatment
Most mild cases resolve without specific therapy; supportive care includes hydration and symptom control. Loperamide is preferred for adults with mild to moderate nonbloody diarrhea but is contraindicated in severe inflammatory diarrhea, bloody diarrhea, C. difficile infection, and in children under two. Bismuth subsalicylate can reduce stool volume in adults and children. Severe or persistent unexplained diarrhea warrants gastroenterology and/or infectious diseases consultation, and cases due to major reportable pathogens or suspected outbreaks should be reported to public health authorities.
In-Patient Considerations
Initial Stabilization
Severe acute inflammatory diarrhea with systemic toxicity requires rapid rehydration and empiric antibiotics.
Admission Criteria
Hospitalize patients with severe dehydration or inability to maintain oral intake.
IV Fluids
Use intravenous volume repletion for severe dehydration or altered mental status.
Discharge Criteria
Discharge is appropriate when fever has been absent for more than 24 hours, vital signs are stable, and the patient can maintain adequate oral fluids and nutrition.
Ongoing Care and Follow-Up
Evaluate and treat household members with similar symptoms when appropriate.
Diet
Resume food about four hours after starting rehydration, using small frequent meals of easily digestible foods, and avoid hyperosmolar fruit juices that can worsen diarrhea.
Patient Education
Counsel on food safety and strategies to prevent foodborne illness, especially during travel.
Prognosis
Gastrointestinal illness contributes to a large burden of hospitalization and death annually in the United States.
Complications
Potential complications include dehydration, electrolyte derangements, bacteremia and sepsis, malnutrition and vitamin loss, hemolytic uremic syndrome, and systemic amebiasis.
Basics
Description
Diarrhea is defined as stool output exceeding 200 g/day and, in practice, as three or more loose stools daily. It is acute when <14 days and chronic when>4 weeks. Inflammatory diarrhea presents with frequent, small-volume stools that are mucoid and/or bloody and may include tenesmus, fever, or severe abdominal pain; stool leukocytes are a key feature. Noninflammatory diarrhea is typically watery, may be high volume (>1 L/day), and occurs without blood, pus, severe pain, or fever.
Epidemiology
Incidence
In the United States, acute diarrhea occurs hundreds of millions of times yearly, with tens of millions of episodes linked to identified pathogens, and foodborne spread accounting for a large proportion of known-pathogen disease. Surveillance data have identified non-typhoidal Salmonella, Campylobacter, Shigella, Cryptosporidium, and Shiga toxin–producing E. coli O157 as leading reported causes, with highest bacterial diarrhea rates from Salmonella, Campylobacter, and Yersinia in infants under one year. Post-diarrheal hemolytic uremic syndrome occurs infrequently overall but is most common in children under five. Traveler’s diarrhea affects a substantial fraction of international travelers.
Risk Factors
Risks include consuming undercooked eggs, meat, poultry, seafood, or unpasteurized dairy, and drinking untreated surface water. Greater severity or pathogen-specific risk occurs with HIV, immunosuppressive therapies (including glucocorticoids, TNF inhibitors, and chemotherapy), recent antibiotic exposure, liver disease, neutropenia, malnutrition, zinc deficiency, and IgA deficiency. Oral–anal sexual contact increases risk of enteric infection. Antibiotic exposure is a major risk factor for Clostridioides difficile–associated diarrhea.
General Prevention
Handwashing before eating or food preparation, avoiding undercooked animal products and unpasteurized dairy, and avoiding untreated stream or river water reduce risk. During travel in areas with unsafe water, avoid tap water and ice. Typhoid vaccination is available for travelers, and infant rotavirus vaccination is recommended in the United States; destination-based vaccine guidance is available through travel medicine resources.
Etiology
Bacterial causes include Campylobacter, Salmonella, Shigella, Yersinia enterocolitica, C. difficile, Vibrio cholerae, Vibrio parahaemolyticus, Aeromonas, Plesiomonas shigelloides, and multiple diarrheagenic E. coli pathotypes including ETEC, EPEC, EIEC, STEC (including O157:H7), and EAEC. Viral causes include rotavirus, human caliciviruses such as norovirus, adenovirus, and cytomegalovirus. Parasitic causes include Giardia intestinalis, Cryptosporidium parvum, Entamoeba histolytica, Cyclospora cayetanensis, Isospora belli, and Strongyloides stercoralis. Toxin-mediated syndromes include Staphylococcus aureus, Bacillus cereus, and Clostridium perfringens.
Diagnosis
History
Evaluation should define likely cause, illness severity, and complications. Ask about travel, diet, antibiotic use, sexual practices, day-care exposure, sick contacts, outbreaks, seasonality, and other illnesses, and characterize stool frequency, duration, and appearance. Infectious diarrhea may include fever, chills, vomiting, nausea, abdominal pain, and tenesmus. Dizziness, presyncope, or syncope suggests volume depletion. Dysentery points to invasive pathogens such as Shigella, Salmonella, Campylobacter, STEC (often without fever), or Yersinia. STEC commonly starts watery and becomes bloody and is frequently associated with contaminated beef or produce; fever is often absent. Yersinia and Salmonella may involve the terminal ileum and cecum, producing right lower quadrant pain that mimics appendicitis. Watery diarrhea alone is nonspecific. Enterotoxin-mediated food poisoning from S. aureus, B. cereus, or C. perfringens typically has a short incubation and brief course, with vomiting alone more typical of S. aureus or C. perfringens and watery diarrhea more typical of B. cereus or C. perfringens; fever is usually absent. Extraintestinal features such as arthritis, skin lesions, or eye symptoms suggest inflammatory bowel disease. With recent international travel, likely pathogens depend on location, setting, and season, commonly including ETEC, EAEC, Campylobacter, Salmonella, and norovirus, and travel medicine resources can guide evaluation.
Physical Examination
Assess blood pressure, heart rate, respiratory rate, temperature, and mental status to gauge severity. Look for dehydration signs such as dry mucous membranes, reduced skin turgor, sunken eyes, delayed capillary refill, low jugular venous pressure, and orthostatic hypotension. Examine for abdominal tenderness, peritoneal signs, hepatomegaly, and splenomegaly.
Diagnostic Tests and Interpretation
Laboratory Studies
Testing is indicated with fever, systemic toxicity, bloody stools, dehydration, suspected foodborne outbreak, recent international travel, immunosuppression, or recent antibiotic exposure. Send stool for culture, noting that routine processing commonly targets Shigella, Salmonella, and Campylobacter, so the laboratory should be alerted if suspicion is high for STEC or other E. coli pathotypes, Yersinia, Vibrio, or other organisms. Stool culture yield is generally low. For bloody diarrhea, culture for Salmonella, Shigella, Campylobacter, and STEC and obtain a Shiga toxin immunoassay; if E. coli is isolated, arrange serotyping via a reference laboratory. If there is recent antibiotic exposure, recent hospitalization, day-care exposure, or recent chemotherapy, test stool for C. difficile toxins. If diarrhea persists beyond seven days, submit multiple stools for ova and parasite examination with attention to Giardia, Cryptosporidium, Isospora, and Cyclospora and consider noninfectious causes; in AIDS or immunosuppression, also evaluate for microsporidia, Mycobacterium avium complex, and cytomegalovirus. Fecal polymorphonuclear cells support an inflammatory process. If dehydration or severe illness is present, obtain electrolytes, renal and liver function tests, complete blood count, and blood cultures.
Imaging
If the diagnosis remains unclear in critical illness, with prominent abdominal pain or peritoneal signs, consider CT abdomen with oral and intravenous contrast.
t
Diagnostic Procedures/Other
Further evaluation may require upper endoscopy or colonoscopy with biopsies
.
Differential Diagnosis
Acute inflammatory diarrhea may be noninfectious, including ulcerative colitis, Crohn disease, radiation or ischemic colitis, partial obstruction, diverticulitis, laxative abuse, rectosigmoid abscess, Whipple disease, pernicious anemia, diabetes-related enteropathy, malabsorption disorders, scleroderma, or celiac disease. Fever and diarrhea can also result from infections outside the gut such as malaria or sepsis.
Treatment
Medications
Core management is rehydration with selective antibiotic use. Oral rehydration is effective and cost-efficient across settings, while intravenous fluids are indicated for severe dehydration or major electrolyte disturbances; rice-based oral solutions are superior for cholera in children and adults. Antibiotics are recommended for severe infection and for persistent gastroenteritis and are favored in adults over 65, immunocompromised patients, those with prosthetic material, and invasive infections, except when STEC is suspected or confirmed. Empiric therapy for febrile community-acquired invasive diarrhea or moderate to severe traveler’s diarrhea includes ciprofloxacin 500 mg twice daily or levofloxacin 500 mg daily while awaiting studies unless STEC is suspected; travel to Southeast Asia raises concern for fluoroquinolone-resistant Campylobacter. For suspected antibiotic-associated or nosocomial diarrhea, treat empirically with metronidazole or vancomycin while awaiting C. difficile testing. Pathogen-directed therapy includes treating non-typhoidal Salmonella in high-risk or severe disease with fluoroquinolones, TMP-SMX, or ceftriaxone for typical short courses and longer courses in immunocompromised patients, recognizing antibiotics may prolong shedding; treating Shigella with short-course fluoroquinolones or TMP-SMX when susceptible and longer courses for severe or immunocompromised cases; treating Campylobacter with erythromycin while acknowledging high fluoroquinolone resistance especially in Southeast Asia; avoiding antibiotics in STEC due to increased HUS risk and providing supportive care; treating ETEC/EPEC/EIEC similarly to traveler’s diarrhea regimens; usually avoiding antibiotics in Yersinia unless severe or immunocompromised, in which case doxycycline plus an aminoglycoside, fluoroquinolones, or TMP-SMX may be used; managing C. difficile by stopping unnecessary antibiotics and using metronidazole for milder disease or oral vancomycin for 10–14 days; prioritizing fluids in cholera with antibiotics guided by local resistance; treating amebiasis with metronidazole followed by a luminal agent such as paromomycin or iodoquinol; treating giardiasis with metronidazole or single-dose tinidazole; and treating Cyclospora or Isospora with TMP-SMX with extended therapy and possible suppression in immunocompromised hosts.
Additional Treatment
Most mild cases resolve without specific therapy; supportive care includes hydration and symptom control. Loperamide is preferred for adults with mild to moderate nonbloody diarrhea but is contraindicated in severe inflammatory diarrhea, bloody diarrhea, C. difficile infection, and in children under two. Bismuth subsalicylate can reduce stool volume in adults and children. Severe or persistent unexplained diarrhea warrants gastroenterology and/or infectious diseases consultation, and cases due to major reportable pathogens or suspected outbreaks should be reported to public health authorities.
In-Patient Considerations
Initial Stabilization
Severe acute inflammatory diarrhea with systemic toxicity requires rapid rehydration and empiric antibiotics.
Admission Criteria
Hospitalize patients with severe dehydration or inability to maintain oral intake.
IV Fluids
Use intravenous volume repletion for severe dehydration or altered mental status.
Discharge Criteria
Discharge is appropriate when fever has been absent for more than 24 hours, vital signs are stable, and the patient can maintain adequate oral fluids and nutrition.
Ongoing Care and Follow-Up
Evaluate and treat household members with similar symptoms when appropriate.
Diet
Resume food about four hours after starting rehydration, using small frequent meals of easily digestible foods, and avoid hyperosmolar fruit juices that can worsen diarrhea.
Patient Education
Counsel on food safety and strategies to prevent foodborne illness, especially during travel.
Prognosis
Gastrointestinal illness contributes to a large burden of hospitalization and death annually in the United States.
Complications
Potential complications include dehydration, electrolyte derangements, bacteremia and sepsis, malnutrition and vitamin loss, hemolytic uremic syndrome, and systemic amebiasis.
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