What is the role of antibiotics in the treatment of Shigella infection?

Updated: Apr 03, 2018
  • Author: Jaya Sureshbabu, MBBS, MRCPCH(UK), MRCPI(Paeds), MRCPS(Glasg), DCH(Glasg); Chief Editor: Russell W Steele, MD  more...
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Answer

The World Health Organization (WHO) recommends that all suspected cases of shigellosis based on clinical features be treated with effective antimicrobials (antibiotics). [24] The choice of antimicrobial drug has changed over the years as resistance to antibiotics has occurred, with different patterns of resistance being reported around the world. Evidence is insufficient to consider any class of antibiotic superior in efficacy in treating Shigella dysentery. The following antibiotics are used to treat Shigella dysentery:

  • Beta-lactams: Ampicillin, amoxicillin, third-generation cephalosporins (cefixime, ceftriaxone), and pivmecillinam (not available in the United States)

  • Quinolones: Nalidixic acid, ciprofloxacin, norfloxacin, and ofloxacin

  • Macrolides: Azithromycin

  • Others: sulfonamides, tetracycline, cotrimoxazole, and furazolidone.

Most clinical infections with S sonnei are self-limited (48-72 h) and may not require antimicrobial therapy.

If an ampicillin and TMP-SMX resistant strain is isolated or if susceptibility is unknown, parenteral ceftriaxone sodium, fluoroquinolone (eg, ciprofloxacin, ofloxacin), azithromycin dihydrate (off-label indication), or oral cefixime are the drugs of choice. [9, 25, 26] Amoxicillin is less effective than ampicillin for treatment of ampicillin-sensitive strains. Oral first- and second-generation cephalosporins are inadequate despite in vitro susceptibility. Recently, Shigella isolates with decreased susceptibility to azithromycin (DSA-Shigella), with minimum inhibitory concentration (MIC) greater than 16 µ g/mL has been described by the CDC. [27]

In June 2015, the Centers for Disease Control and Prevention (CDC) warned that they received reports of infections with Shigella strains that are not susceptible to ciprofloxacin and/or azithromycin.  CDC is seeing resistance to ciprofloxacin in 1.6% of the Shigella cases tested and resistance to azithromycin in approximately 3%. The CDC added that most cases have been reported among gay, bisexual, and other men who have sex with men in Illinois, Minnesota, and Montana and among international travelers, but cases are also occurring among other populations. [28, 29, 30]

Because shigellosis is self-limiting, some authorities recommend withholding antibiotic therapy. When an effective antibiotic is given, clinical improvement is anticipated within 48 hours. This lessens the risk of serious complications and death, shortens the duration of symptoms, and hastens the elimination of Shigella and the subsequent spread of infection. The risk of continued shedding of organisms in stool increases the risk of transmission of further disease among contacts argues against withholding antimicrobial treatment. [31]

Antimicrobial therapy is typically administered for 5 days. Antibiotic treatment decreases the duration of illness, person-to-person spread, and cases in household contacts. Treatment in malnourished children (eg, in developing countries) is likely to reduce the risk of worsening malnutrition morbidity after shigellosis. In persons infected with S dysenteriae type 1, early administration of effective antibiotics decreases Shiga toxin (Stx) concentrations in the stool and lowers HUS risk. However, the risk of HUS caused by E coli O157-H7 may be increased with the early administration of antibiotics. Prophylactic antibiotics are not recommended for contacts.

Antidiarrheal medications (diphenoxylate hydrochloride with atropine [Lomotil] or loperamide [Imodium]) should not be used because of the risk of prolonging the illness. WHO has introduced the use of zinc for 10-14 days as part of a diarrheal disease control program in addition to oral rehydration therapy. Initiating zinc at the time of diarrhea leads to shorter duration and fewer loose stools. [21, 32]

A child with typical dysentery that responds to initial empirical antibiotic treatment should continue taking the same drug for a full 5-day course, even if the stool culture is negative.


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