Page 104 - JSOM Winter 2017

An Ongoing Series

Shigellosis

Mark W. Burnett, MD

Introduction
Shigellosis is the most common cause of dysentery worldwide.
Across the globe, more than 165 million cases of severe infec-
tion cause more than 1 million deaths annually, most often in
the poorest countries and most often affecting children. More
than 125 million of these infections occur in Asia alone. In the
United States, there are an estimated half-million cases occur-
ring each year, which makes shigellosis one of the most com-
mon causes of bacterial enteric disease nationally.

Four main species, with more than 40 different serotypes, of
Shigella exist. Shigella is a gram-negative bacillus of the fam- Shigella bacterium.
ily Enterobacteriaceae. S. flexneri is the most common spe- occur in infants and children who are malnourished. Seizures
cies worldwide, although S. dysenteriae is a frequent cause of are also seen in children with shigellosis, usually while they are
outbreaks in resource-limited countries. S. sonnei, the most febrile. Shiga toxin released by S. dysenteriae serotype 1 dam-
common cause of shigellosis in the United States and Western ages the renal vasculature, sometimes resulting in hemolytic
Europe, is becoming an increasingly important cause of dys- uremic syndrome, which may result in life-threatening renal
entery worldwide for reasons that are not entirely understood. failure in both children and adults.

Although a variety of primates can be infected with Shigella Diagnosis
spp., humans are the natural host and the propagator of out-
breaks. One of the unique features of Shigella infections is the The diagnosis of shigellosis classically has been made by the
small amount of inoculum that can cause disease: Ingestion of isolation of the organism in culture from the stool or, in more
as few as 10 organisms can cause illness. The primary route severe cases, from the blood. Recently, multiplex polymerase
of transmission is fecal-oral; the bacterium can be ingested chain reaction testing has been approved that can shorten the
through food and water, can be carried by flies, and can be time to diagnosis, but these testing modalities are expensive
transmitted by handling contaminated inanimate objects. Shi- and not often found in the developing world. In a field setting,
gella may be isolated from infected persons while they have the diagnosis of a Shigella infection will likely be made clini-
diarrheal stools, and for weeks after their diarrhea has re- cally. In areas of the world where amoebic dysentery caused
solved. This, coupled with the fact that Shigella can survive by Entamoeba histolytica is prevalent, this too must be con-
in untreated water for up to 6 months and in food for up to sidered in the differential diagnosis. Broad-spectrum antimi-
30 days, may result in prolonged and devastating outbreaks crobial therapy is started for treatment if definitive diagnostic
in situations where refugee or internally displaced persons are testing is unavailable.
living in close confines.
Treatment
Clinical Presentation
Oral rehydration and supportive measures are the most vital
Shigella primarily infects the large intestine and can cause a aspect of care in shigellosis. In healthy individuals, the illness
range of symptoms. After ingestion of the organism and an is usually self-limited, and symptoms resolve within 72 hours.
incubation period of typically 1 to 2 days, patients develop di- Antibiotic therapy (ciprofloxacin, azithromycin, and cefixime
arrhea, high fevers, abdominal pain, cramping, and tenesmus. are effective) has been shown to shorten the duration of the
The diarrheal stools can become dysenteric, containing gross diarrheal episodes as well as the shedding of the organisms
blood and mucus. Infections of the blood most commonly in the stool. Intravenous therapy (e.g., ceftriaxone) should be

COL Burnett is currently chief of pediatric infectious diseases at Tripler Army Medical Center, Honolulu, HI, and is the pediatric
subspecialties consultant to the US Army Surgeon General. He is board certified in pediatrics and pediatric infectious diseases.

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