TOC |  GI-Disorders  |  Medline Drugs Info  

Infectious Diarrhea or Colitis 

Clostridium difficile diarrhea & colitis                               REF:  Clostridium2010.pdf      
C.difficile is a noninvasive Gram positive, sore-forming, ibligate anaerobid bacillus, which produce toxins A & B.
It can be cultured from the stool in 5 % of healthy adults, in 10-30% of asymptomatic hospital & nursing patients. Therefore, the mere presence of C.difficile does not necessarily indicate disease.
Antibiotics most frequently associated with this infection are clindamycin, ampicillin, amoxicillin, and cephalosporins, but all antibiotics may predispose patients to C difficile infection.

The clinical presentation varies from asymptomatic colonization to mild diarrhea to severe debilitating disease, with high fever, leukocytosis, severe abdominal pain, paralytic ileus, colitis (pseudomembrane), colonic dilation (or toxic megacolon), or even perforation; rare extraintestinal manifestation as perianal abscesses, bacteremia, & seeding of prosthetic joints.

The most sensitive and specific test available for diagnosis of C difficile infection is a tissue culture assay for the cytotoxicity of toxin B. However, this test takes 1 to 3 days to complete and requires tissue culture facilities. Detection of C difficile toxin by means of enzyme-linked immunoassay is more rapid and inexpensive. A minority of patients may require more than 1 stool assay to detect toxin.

  • C.difficile diarrhea is defined by recent antibiotic use, evidence of toxin-producing strains of C.difficile, & in select cases, by visualizing pseudomembranes on endoscopy or a pathologic specimen.
  • The presence of C. difficile may be documented by:
    • C.difficile stool culture
    • The enzyme immunoassay , latex agglutination test, for the C.difficile toxin

Approximately 15% of patients experience relapse after initial therapy and require retreatment, sometimes with an extended, tapering regimen. Immunity appears to be incomplete and predominantly mediated by serum IgG to toxin A.

  1. Stop the offending antibiotic if possible
  2. Replace fluids & electrolytes
  3. Antibiotics: Oral metronidazole (Flagyl)  250mg qid -500 mg tid or vancomycin 125 mg qid for 10-14 days.   


Prophylaxis of traveler's diarrhea has been a hotly contested issue for many years. Although several antibiotics have been shown to be of benefit in preventing this illness (e.g., doxycycline [Vibramycin], trimethoprim-sulfamethoxazole [Bactrim], norfloxacin * [Noroxin], ciprofloxacin [Cipro]), the routine use of these agents for prophylaxis is generally not recommended.  Arguments against prophylaxis include the side effects of antimicrobial therapy (e.g., skin rashes including erythema multiforme, vaginal candidiasis, photosensitivity reactions, bone marrow toxicity, and anaphylaxis). In addition, altering gut flora may predispose to resistant pathogens.

Empirical antibiotic therapy  for traveler's diarrhea
can be recommended after the third loose stool in a 24-hour period and in patients who have diarrhea associated with severe abdominal pain, fever, or dysentery.  
Fluoroquinolone antibiotics (as Cipro 500 mg bid PO)  remain the drugs of choice for adults with traveler's diarrhea in all areas other than in inland Mexico, as widespread resistance of E. coli to usual agents such as trimethoprim-sulfamethoxazole is present elsewhere. In inland Mexico trimethoprim-sulfamethoxazole remains effective.


Campylobacter jejuni Colitis Rx:
- usually self-limited with no treatment needed except for symptomatic relief, e.g. bismuth subsalicylate (Pepto-Bismol)
- supportive treatment with attention to fluid and electrolyte balance may be needed in more severe cases
  • Drug of Choice: Erythromycin 500 mg qid x 5 days or Azithromycin 500 mg daily x 3 days
  • Ciprofloxacin (Cipro) 500 mg bid PO x 5 days (Norfloxacin, 400 mg ; ofloxacin, 400 mg ; ciprofloxacin, 500 mg PO)
  • Vibramycin 100 mg bid

Shigellosis Rx:

  • Ciprofloxacin (Cipro) 500 mg bid PO x 5 d (Norfloxacin, 400 mg ; ofloxacin, 400 mg ; ciprofloxacin, 500 mg PO)
  • Septra-DS bid  (recent resistant strains noted)
  • Amoxicillin 500 mg tid   (recent resistant strains noted)

Salmonella Gastroenteritis Rx:

  • Rx usually not required (see text)
  • Oral Ciprofloxacin (Cipro) 500 mg bid x 3-5 d (Norfloxacin, 400 mg ; ofloxacin, 400 mg ; ciprofloxacin, 500 mg PO)

Yersinia -induced diarrhea Rx:

  • Oral Ciprofloxacin (Cipro) 500 mg bid  for 7-10 d (Norfloxacin, 400 mg ; ofloxacin, 400 mg ; ciprofloxacin, 500 mg PO).
  • TMP-SMX or doxycycline
  • Antibiotic therapy only in severe (systemic) cases

Enterotoxic Escherichia coli diarrhea Rx:

  • Oral Ciprofloxacin (Cipro) 500 mg bid  for 3d
  • doxycycline 100 mg bid
  • furazolidone

Vibrio cholerae Rx:

  • Doxycycline 100 mg bid
  • TMP-SMX or
  • ampicillin


  • Metronidazole  (Flagyl) 750 mg PO tid for 10 d
  • Dehydroemetine 1-1.5 mg/kg/d IM for 5 d
  • Both plus a luminal amebicide (iodoquinol [Yodoxin], 650 mg PO tid × 20 d; paromomycin, 500 mg PO tid × 7 d) for invasive intestinal infection and hepatic abscesses : cyst passers without symptoms require luminicidal agent only


  • Metronidazole (Flagyl) 250 mg PO tid for 5 to 10 days (15 mg/kg/day in 3 doses in children for 5 days - DynaMed 2009 ); or
  • Tinidazole (Tindamax) 2 gm single dose; used only for metronidazole-resistant case; advise againt alcohol use during and 3 days after Tinidazole use.
  • quinacrine hydrochloride 100 mg tid x 5 days (2 mg/kg in children)
  • furazolidone (Furoxone) 100 mg qid (6mg/kg/day in 4 doses in children) for 7 - 10 days
  • paromomycin aminosidine, (Humatin) 25-35 mg/kg/day in 3 doses for 7 days.
  • Relapses may occur


  • Paromomycin (Humatin), 500 mg PO bid
  • Azithromycin,
  • hyperimmune bovine colostrum,
  • Nitazoxanide
  • Benefit and duration of any therapy unclear; spontaneous resolution without specific therapy in immunocompetent hosts and in HIV-infected individuals with CD4 counts > 150 cells/mm3


  • Albendazole 200-400 mg PO bid × 3 mo
  • Albendazole more effective for Encephalitozoon intestinalis than for Enterocytozoon bieneusi; available for  compassionate use only


  • TMP-SMX 1 DS PO qid × 10 d, then bid for 3 wk
  • Pyrimethamine + folinic acid
  • Maintenance therapy required in patients with AIDS


  • TMP-SMX 1 DS PO bid × 3-5 d


For those patients with diarrhea of 2-3 days' duration, work-up is rarely necessary unless fever, bloody diarrhea, or severe abdominal pain is present.

Viruses are the major cause of gastroenteritis in the United States and indeed worldwide, accounting for up to 30% to 40% of acute episodes. There is limited utility in doing special viral cultures because specific viruses are rarely isolated, and knowing the identity of the virus does not alter management.

Patients with small-volume, bloody diarrhea and lower abdominal cramping and tenesmus are likely to have colitis. When diarrhea is the result of an infection, invasive bacteria are the most likely cause.  

Large-volume, watery diarrhea and diffuse abdominal cramps are typical of small intestinal infection.

A detailed history of recent travel (within 6 months), recent antibiotic use (within 6-8 weeks), contact with individuals who are ill, and specific dietary ingestions during foodborne outbreaks can suggest an infectious etiology.  

  • Individuals who have reported drinking from unpurified stream water in mountainous regions should be tested for Giardia lamblia.
  • Stool should be tested for Clostridium difficile if diarrhea develops during or after recent hospitalization or antibiotic use.
  • In foodborne or waterborne outbreaks of diarrhea, the incubation period can often suggest the cause of the outbreak. When symptoms occur within 6 hours of eating, ingestion of the preformed toxin of Staphylococcus aureus or Bacillus cereus should be suspected. If the symptoms occur within 8-14 hours of ingestion, Clostridium perfringens should be suspected.
  • While infectious agents do not commonly cause chronic diarrhea, those that do include Escherichia coli, C difficile, Giardia, Entamoeba histolytica, Cryptosporidium, Aeromonas, and Yersinia enterocolitica.   Infection with HIV is also a common cause of diarrhea.

Because symptoms generally resolve within 24-48 hours, most patients with acute infectious diarrhea will not require any specific treatment. The primary therapy for all patients in this setting is oral hydration.  Patients with dysentery (bloody diarrhea) require evaluation because this population may benefit from antimicrobial therapy.

Fever and dysentery are often due to infection by an invasive organism, such as Salmonella, Shigella, Campylobacter, enteroinvasive and enterohemorrhagic E coli, Aeromonas spp, some noncholera vibrios, or amebiasis.  Patients with acute onset of diarrhea with fever and either blood in their stools or evidence of fecal leukocytes should be given empiric antibiotic therapy. The drug of choice in this clinical setting is a quinolone antibiotic as Ciprofloxacin (because the most likely organisms to be isolated are generally susceptible to the quinolones). Once a specific pathogen is isolated and sensitivities to antibiotics are identified, therapy can be modified as needed.

Organism & The Recommended Antimicrobial Treatment  for Infectious Diarrhea

  • Vibrio cholerae: Tetracycline or trimethoprim-sulfamethoxazole (erythromycin if resistant to tetracycline), ciprofloxacin (Cipro), norfloxacin, doxycycline
  • Vibrio parahaemolyticus:  None
  • Aeromonas:  Chloramphenicol, ciprofloxacin, aminoglycosides, third-generation cephalosporins, aztreonam, imipenem
  • Plesiomonas shigelloides:  Chloramphenicol, aminoglycosides, trimethoprim-sulfamethoxazole, fluoroquinolones, tetracycline, third-generation cephalosporins, imipenem
  • Shigella: Ampicillin, trimethoprim-sulfamethoxazole (ciprofloxacin or cefixime for resistant strains)
  • Salmonella species (except S typhi; see below):  None unless severe disease with systemic compromise, then ciprofloxacin
  • Salmonella typhi:  Chloramphenicol or ampicillin, trimethoprim-sulfamethoxazole, third-generation cephalosporins, ciprofloxacin
  • Campylobacter:  None unless there is severe disease or in the case of debilitated patients, then erythromycin
  • Yersinia:  None unless severe disease, then ceftriaxone
  • Listeria monocytogenes:  Ampicillin, trimethoprim-sulfamethoxazole
  • Enterotoxigenic Escherichia coli : Trimethoprim-sulfamethoxazole
  • Enteropathogenic E coli : Ampicillin or trimethoprim-sulfamethoxazole
  • Enteroinvasive E coli : None unless severe cases, then ciprofloxacin
  • Enterohemorrhagic E coli : None; even in severe cases there is unclear benefit from antimicrobials
  • Mycobacterium tuberculosis:  Isoniazid, pyrazinamide, rifampin
  • Giardia lamblia : Metronidazole (Flagyl) , furazolidone, albendazole. Paromomycin is drug of choice for pregnant women
  • Entamoeba histolytica : Metronidazole (Flagyl)
  • Schistosoma spp:  Praziquantel
  • Strongyloides stercoralis:  Thiabendazole, ivermectin, mebendazole
  • Trichuris trichiura:  Mebendazole
  • Cryptosporidium: None unless persistent infestation beyond 2 weeks, then paromomycin
  • Isospora belli:  Trimethoprim-sulfamethoxazole, pyrimethamine
  • Cyclospora cayetanensis:  Trimethoprim-sulfamethoxazole

The most critical therapy in diarrheal illness is hydration, preferably with oral rehydration solution (ORS).  The composition of this fluid is 90 mm sodium, 80 mm chloride, 111 mm glucose, and 10 mm citrate (or bicarbonate) per liter. Whereas antibiotic therapy is indicated only in a small number of instances, hydration remains the mainstay of diarrheal therapy.

In general, antimicrobial therapy is indicated in the following situations: treatment of infectious colitis due to Shigella, diarrhea due to C. difficile, cholera, traveler's diarrhea, amebiasis, and giardiasis.

Gastroenteritis due to nontyphoidal Salmonella is usually self-limited (diarrhea lasting longer than 1 week should suggest an alternative diagnosis), and therefore antibiotic therapy is not indicated. It may, in fact, prolong carriage and lead to an increased rate of relapse in children. However, treatment should be strongly considered in newborns (to prevent meningitis); in patients older than 50 (especially those with atherosclerosis); in immunosuppressed patients (e.g., persons who have AIDS, organ transplant recipients); in patients with inflammatory bowel disease; and in patients with bone and joint prostheses, chronic arthritides, and hemoglobinopathies.

Antibiotic therapy may be withheld in most cases of diarrheal illness due to the other major bacterial enteric pathogens, as these are self-limited illnesses. Antibiotic therapy may be indicated in patients who present with high fever, bloody diarrhea, more than eight stools per day, dehydration, and symptoms for more than 1 week and in immunocompromised patients.  Empirical antibiotics may be given to prevent the need for hospitalization in ill patients.