Causative Agent

Routes of Exposure

Infective Dose & Infectivity

Incubation Period

Clinical Effects

Lethality

Transmissibility

Primary Contaminations & Methods of Dissemination

Secondary Contamination & Persistence of organism

Decontamination & Isolation

Laboratory testing

Therapeutic Treatment

Prophylactic Treatment

Differential Diagnosis

References

Causative Agent: Several distinct bacteria within the genus Salmonella cause diarrheal illness, sometimes with septicemia.  Salmonella enteritidis has more than 2000 different serotypes and is responsible for many of the foodborne gastrointestinal illnesses commonly found in man and animals.  Salmonella typhi causes typhoid fever. 

Routes of Exposure: Oral - consumption of contaminated food or water

Infective Dose & Infectivity: The infective dose is unknown but the LD₅₀ has been reported to be 10 million organisms. The infectivity of Salmonella is moderate.  A carrier state occurs and is more common among female and elderly patients.  It may persist for months to years. 

Incubation Period: The incubation can be from 6 to 72 hours, but it usually ranges from 12 to 36 hours.

Clinical Effects: Salmonella gastroenteritis typically manifests as nausea, vomiting, abdominal cramps, and diarrhea, which is sometimes bloody.  Weakness, chills, and fever may also be present, although there is a wide variability in the severity of symptoms seen.  The typhoidal syndrome includes a high spiking fever, abdominal cramps, diarrhea, abdominal distention, septicemia, enlarged spleen, and occasional meningeal signs.

Lethality: The mortality rate of salmonellosis is low to moderate (<1% for most serotypes).

Transmissibility: The fecal-oral route is the most common mode of person-to-person transmission.  There is no known transmission by the inhalational or dermal routes. 

Primary Contamination & Methods of Dissemination:

In a terrorist attack, salmonellosis would most likely occur due to intentional contamination of food or water supplies.

Secondary Contamination & Persistence of Organism:  Secondary transmission can result from exposure to the stool of patients with overt disease and from chronic carriers.  Diarrheal fluids are highly infective.  Greater than 50% of patients stop excreting nontyphoidal Salmonella within five weeks after infection and 90% are culture negative within nine weeks.

Decontamination & Isolation:

• Patients – No decontamination necessary.  Patients can be treated with standard precautions, with contact precautions for diapered or incontinent patients.  Hand washing is of particular importance

• Equipment & other objects – 0.5% hypochlorite solution (one part household bleach and nine parts water), other disinfectants, and/or soap and water are effective for environmental decontamination. 

Laboratory testing: The stool, blood, and ingested food can be cultured.   The best clinical predictor of a positive stool culture for Salmonella is the combination of diarrhea persisting for more than 24 hours, fever, and either blood in the stool or abdominal pain with nausea or vomiting.

Therapeutic Treatment: For uncomplicated cases, rehydration may be all that is required.  Oral or intravenous routes  for rehydration can be used depending on the individual patient’s circumstances.  Antibiotics are not ordinarily used since they prolong fecal shedding, but they should be considered in infants, the elderly, and those with underlying illnesses.  All bacteremic patients should receive antibiotics. 

Strains from developing countries are often resistant to many antibiotics, but are usually susceptible to fluoroquinolones (such as ciprofloxacin or levofloxacin) or third generation antibiotics (such as cefotaxime or ceftriaxone).   More narrow antibiotics (such as ampicillin, amoxicillin, and trimethprim-sulfamethoxazole) are alternatives choices when the strain is known to be susceptible.

Prophylactic Treatment:  A typhoid vaccine exists.  It is recommended for travelers to areas where there is a risk of exposure to Salmonella typhi, people living in typhoid-endemic areas outside the United states, persons who have continued household contact with a documented typhoid fever carrier, and laboratory workers with frequent contact with S. typhi.  No prophylaxis is recommended for nontyphoidal Salmonella infections.

Differential Diagnosis: Shigella, Campylobacter, Yersinia enterocolitica, and bacterial food poisoning may show similar signs and symptoms. 

References:

• Chin J. Control of Communicable Diseases Manual, Seventeenth Edition, American Public Health Association; 2000.

• American Academy of Pediatrics.  Salmonella.  In:  Pickering LK, ed.  Red Book:  2003 Report of the Committee on Infectious Diseases.  26 ed.  Elk Grove Village, IL:  American Academy of Pediatrics; 2003: 541-547.

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