Bacteremia at Boston City Hospital: Occurrence and Mortality during 12 Selected Years (1935-1972), with Special Reference to Hospital-Acquired Cases

Abstract

The cases of all patients hospitalized at Boston City Hospital during 1972 who had blood cultures positive for a clinically significant, aerobic bacterial pathogen or for Candidawere analyzed with respect to incidence and mortality, sex, age, admission to medical or surgical services, and the causative organism. Similar data were obtained for 11 years between 1935 and 1969 selected to reflect the introduction and general use of various effective antibacterial agents. Comparisons were also made between hospital-acquired bacteremic infections (defined as those in which the first positive blood culture was obtained on or after the third day in the hospital) and community-acquired infections (defined as those with positive blood cultures on admission or within the first two days in the hospital). In 1972, the incidence of bacteremic infections (but not the case-fatality ratio) was significantly higher in males than in females. Bacteremic infections were more than twice as frequent on the medical than on the surgical services, but the case-fatality ratio was slightly but not significantly higher on the surgical services. Bacteremia was most frequent in the youngest (birth through nine years) and the oldest (~60 years) age groups, whereas the case-fatality ratio was lowest in the youngest group and increased with each decade of life. Streptococcus pneumoniaewas the most frequent organism causing bacteremia; next were Escherichia coli, Klebsiella-Enterobacter, and Staphylococcus aureus, in that order. The case-fatality ratio was lowest in cases due to S. pneumoniae and highest in those caused by Pseudomonas aeruginosa, Proteus, and Klebsiella-Enterobacter. The data for all 12 selected years indicate a rising incidence of bacteremic infections during the 1950s and most of the 1960s, with evidence of decline in 1969 and 1972. The greatest proportion ofbacteremic cases on the medical services were community-acquired, whereas the majority of those on the surgical services were hospital-acquired; on both the medical and the surgical services, the rates of hospital-acquired infections continued to increase, and most of the recent decrease was in community-acquired cases on medical services. Case-fatality ratios were significantly higher among those with hospital-acquired infections than among those with community-acquired infections in all instances. In 1935 about one-fifth of all cases of bacteremic infection and about 30% of deaths from such infections were in patients ~60 years old. The remaining cases were about equally divided among those <30 years old and those 30-59 years old, but one-half of all deaths were among the latter age group. In the ensuing years the proportion of cases (and particularly of deaths) in those <30 years old declined sharply, whereas cases and deaths in patients ~60 years old increased to about one-half of all cases and to more than 60% (up to three-fourths) of all deaths in each of the selected years. In 1935, S. pneumoniaeand β-hemolytic Streptococcusaccounted for more than half of all cases of bacteremic infection and for nearly two-thirds of all deaths from such infections; S. aureusaccounted for one-fifth of the cases and for one-sixth of the deaths. During the 1950s, the number of S. aureusinfections increased until this organism accounted for more than one-third of the bacteremic cases and deaths, but these proportions decreased in ensuing years to only one-eighth of all cases and deaths. Gram-negative bacilli have accounted for increasing proportions of cases since 1951 and now predominate as causes of bacteremic infection and of deaths from such infections.