Influence of splenectomy on lethal effects of pneumococcal infection

To determine whether the splenectomized host is more sensitive to the toxic effects of pneumococcal infection and whether the known clearance defect accounts for the early, increased mortality seen in postsplenectomy infection, the authors studied 8-week-old C57B1 mice. They were divided into two groups: seven control nonsplenectomized mice and six splenectomized mice. All animals were inoculated intravenously with 10(3) colony forming units of Streptococcus pneumoniae. Microaliquots of blood were drawn from the tail of all mice into sterile, heparinized, capillary tubes at 1, 4, 8 and 16 hours. Blood bacteria were quantitated using a drop dilution method. The time to death was recorded. A form of survival analysis using the Cox proportional hazards model was performed on the data. The infection was uniformly fatal. An early decrease in the numbers of blood bacteria was seen in nonsplenectomized mice followed by a logarithmic linear increase. In splenectomized mice, there was early rapid bacterial growth greater than that in control mice. Splenectomized mice died earlier than control mice (p less than 0.05 at 24 hours, Fisher's exact test). The bacterial count had a highly significant effect upon mortality overall (p = 0.0017). A function describing the risk of dying versus bacterial numbers was generated and was the same for both groups. The splenectomized host does not appear to be more susceptible to the toxic effects of pneumococcal infection. Early mortality in bacteremic pneumococcal infection can be attributed to impaired bacterial clearance alone.