Prediction ofmicrobial aetiology atadmission to hospital forpneumonia fromthepresenting clinical

Theselection ofinitial antimicrobial treatment inapatient withcommunity acquired pneumonia isanimportant clinical decision. Because this decision isusually madebefore theresults ofspecific microbiological tests areavailable, we attempted todetermine howwellthepresenting clinical features wouldallow prediction ofmicrobial aetiology in441adults admitted tohospital with pneumonia. Fiveof90variables available onadmission wereselected forinclusion inamultivariate discriminant function analysis because oftheir strong association withone ormore ofthemajor aetiological subsets (Mycoplasma pneumoniae, Streptococcus pneumoniae, "other," andunde- termined). Thesevariables were age,numberofdaysill before admission, presence orabsence of bloody sputumandoflobar infiltration on chestradiograph, andwhitebloodcell count.The microbial aetiology was correctly predicted bythis discriminant function analysis inonly42%of cases,whichgives aquantitative estimate ofthedegree ofdifficulty encountered indetermining the microbial aetiology atthetimeofadmission forpneumonia. Whenasimilar discriminant function analysis wasapplied tothethird ofpatients inwhomthemicrobial aetiology was neverdetermined, mostofthese caseswerepredicted tobeduetoStreptococcus pneumoniae.