Clinical prediction model for differentiation of disseminated histoplasma capsulatum and Mycobacterium avium complex infections in febrile patients with AIDS

Background: Disseminated infection with Histoplasma capsulatum and Mycobact erium avium complex (MAC) in patients with AIDS are frequently difficult to distinguish clinically. Methods: We retrospectively compared demographic information, other opportu nistic infections, medications, symptoms, physical examination findings and laboratory parameters at the time of hospital presentation for 32 patients with culture documented disseminated histoplasmosis and 58 patients with d isseminated MAC infection. Results: Positive predictors of histoplasma infection by univariate analysi s included lactate dehydrogenase level, white blood cell (WBC) count, plate let count, alkaline phosphatase level, and CD4 cell count, By multivariate logistic regression analysis, those characteristics that remained significa nt included a lactate dehydrogenase value greater than or equal to 500 U/L (risk ratio [RR], 42; 95% confidence interval [CI], 18.53-97.5; p < .001), alkaline phosphatase less than or equal to 300 U/L (RR, 9.35: 95% CT. 3.61- 33.48: p = .008), WBC less than or equal to 4.5 x 10(6)/L (RR, 21.29: 95% C I, 6.79-66.75; p = .008), and CD4 cell count (RR, 0.958; 95% CI, 0.946-0.97 1; p = .001). Conclusions: A predictive model for distinguishing disseminated histoplasmo sis from MAC infection was developed using lactate dehydrogenase and alkali ne phosphatase levels as well as WBC count. This model had a sensitivity of 83%, a specificity of 91%, and a misclassification rate of 13%.