salmonella

This patient most likely has typhoid fever, also known as enteric fever, caused by either of the typhoidal Salmonella strains, S. typhi or S. paratyphi. Infection is transmitted by ingestion of food or water contaminated by feces. In resource-poor areas, organisms may be spread in community food or, more frequently, by water. In developed countries, transmission is chiefly by food that has been contaminated during preparation by healthy carriers. Symptoms of enteric fever are generally nonspecific. Fever is the major manifestation, typically rising over 2 to 3 nights and persisting for several days. A pulse-temperature dissociation (relative bradycardia) is often present. A brief period of diarrhea followed by constipation, abdominal discomfort, nonproductive cough, mild confusion, and transient small blanching skin lesions (rose spots) are other clinical features. Ceftriaxone is the preferred empiric antibiotic agent, with ciprofloxacin and azithromycin as additional options if resistance is not encountered.

Human brucellosis can develop after exposure to one of four Brucella species through contact with viable organisms in secretions or excretions of infected animals, ingestion of undercooked meat or milk products, or, less often, inhalation. Patients experience numerous nonspecific symptoms as well as recurring or “undulating” waves of fever, but rash, gastrointestinal symptoms, and relative bradycardia are not typical.

Salmonella typhi and Salmonella paratyphi (A, B, and C) cause prolonged febrile and often serious infection (typhoid fever). Infection is acquired by consuming food or water contaminated by organisms shed in the stool of infected humans. Travel to South, East, and Southeast Asia (Indian subcontinent) and portions of sub-Saharan Africa pose the greatest risk of infection. Unlike other nontyphoidal Salmonella (see Infectious Gastrointestinal Syndromes), the causative agents of enteric fever are human-only pathogens. Oral and parenteral vaccines (see Table 41) afford temporary protective immunity in 50% to 80% of recipients.

The gradual onset of fever with headache, arthralgia, myalgia, pharyngitis, and anorexia follows a 1to 2-week incubation period. Abdominal pain and tenderness can be accompanied by early-onset diarrhea, which may spontaneously resolve or become severe late in disease. One fifth of patients have constipation at diagnosis. In untreated illness, temperature progressively increases and may remain elevated (up to 40 °C [104 °F]) for 4 to 8 weeks. A pulse-temperature dissociation (relative bradycardia) and prostration are common. During the second week of illness, discrete, blanching, 1to 4-mm salmon-colored macules, known as rose spots (Figure 19) develop in crops on the chest and abdomen in about 20% of patients. Moderate hepatosplenomegaly, leukopenia, anemia, thrombocytopenia, and elevated aminotransferase levels are common. Secondary bacteremia may cause pyogenic complications such as empyema, muscle abscess, and endovascular infections. Intestinal hemorrhage or perforation may occur 2 to 3 weeks after infection onset. Encephalopathy occurs in more severe cases.

Invasion of the gallbladder by typhoid bacilli may result in a long-term carrier state with shedding of organisms in the stool for more than 1 year. Those with gallstones and chronic biliary disease are at greatest risk.

Diagnosis is made through isolation of S. typhi or S. paratyphi from blood, stool, urine, or bone marrow; isolation success declines after the first week of illness. Rapid serologic tests are available to distinguish Salmonella enterica serotype typhi antibodies.

Antibiotic treatment decreases mortality and shortens the duration of fever. The emergence of antibiotic resistance in many geographic areas necessitates that in vitro susceptibility testing be performed on all clinical isolates. Ceftriaxone, fluoroquinolones, and azithromycin are preferred treatments. Dexamethasone has been shown to decrease mortality in severe illness, such as in patients with shock and encephalopathy. A 28-day course of ciprofloxacin is effective in eradicating chronic carriage, although cholecystectomy may be needed in cases of cholelithiasis.

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