The PCR of saliva is the preferred diagnostic test for confirming rabies in humans because it directly detects the presence of rabies viral RNA in body fluids during the early symptomatic phase. Serum antibody tests are not reliable in the acute phase as antibodies may take time to develop, and CSF analysis is nonspecific. PCR offers high sensitivity and specificity, enabling timely and accurate diagnosis essential for patient management and public health interventions. Urine culture is irrelevant for rabies diagnosis since rabies virus is not excreted in urine.

Reference: Harrison's Principles of Internal Medicine, Kasper et al., 20th Edition.