IgM antibody response to staphylococcal infection.

Of patients with staphylococcal infections, high levels of IgM antibodies of staphylococci measured by radioimmunoassay were present in 13 of 17 patients with endocarditis, nine of 23 with complicated bacteremia, one of 20 with uncomplicated bacteremia, and two of 21 with nonbacteremic infections. Of control subjects, high levels of IgM antibodies were present in seven of 26 individuals with gram-positive infections, two of 16 with gram-negative infections, two of 20 with rheumatoid arthritis, and two of 50 uninfected persons. Concomitant elevation of IgG and IgM antibody levels occurred in 20 of 40 patients with endocarditis or complicated bacteremia compared with two of 41 patients with other types of staphylococcal infections and three of 112 control subjects. IgM antibodies only were present early in the infection in six of 13 patients with staphylococcal endocarditis or complicated bacteremia. IgG or IgM antibody levels remained elevated at least four weeks after initiation of treatment.