An infant rat model of bacteremia with Brazilian purpuric fever isolates of Hemophilus influenzae biogroup aegyptius. Brazilian Purpuric Fever Study Group.

Brazilian purpuric fever (BPF) is a newly recognized fulminant pediatric infection caused by bacteremia with Hemophilus influenzae biogroup aegyptius (Hae). Following intraperitoneal inoculation, each of five disease isolates caused bacteremia more frequently than control, conjunctival isolates of Hae in complement-depleted 6-d-old rats. Sustained but self-limited bacteremia was observed in normal infant rats after inoculation with a disease strain. These rats developed meningitis and had depressed hemoglobin concentration and platelet counts. Pathologic examination showed meningitis and contiguous otitis. Pretreatment of infant rats with immune adult rat serum raised against disease isolates protected rats from bacteremia. Normal adult rat serum or immune rat serum against control strains failed to protect infant rats. Thus, strains of Hae isolated from patients with BPF are more virulent than control strains. Antibody against antigens unique to disease isolates protects infant rats from bacteremia.