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A retrospective epidemiological study was conducted in connection with an outbreak of paratyphoid fever at a Peruvian naval installation in Callao. The study sought to determine the magnitude of the outbreak, the source of infection, the attack rates, the persistence of bacilli excretion, and the clinical picture of the disease. The source of Salmonella paratyphi B infection had been a meal of chicken and rice served to around 400 members of the naval police. Over a period of three weeks, 21 persons were hospitalized and 52 received outpatient treatment at the naval hospital. In addition, through a questionnaire it was revealed that 86 unreported cases of diarrhea related to the outbreak had occurred. The most common clinical manifestations were fever, headache, weakness, anorexia, abdominal pain, and diarrhea. The general attack rate was 39.8%. In a follow-up survey carried out 37 days after exposure, fecal cultures indicated that 8.5% of the persons affected continued to excrete the microorganism. The high rates of attack and transmission of S. paratyphi B in this outbreak point up the considerable pathogenicity and virulence of some strains of the microorganism and their impact on public health. It is suggested that preventive measures be taken at naval and other similar installations, including the education of workers who handle and prepare food, in order to ensure proper hygiene.