In situations where there is suspicion of infection based on indirect evidences of infection like leucocytosis (or leucopenia in neonates), acute phase reactants (like CRP, Calcitonin, etc.), radiology (consolidation on X-ray), and exudates (pleural fluid, CSF, joint aspirates, abscesses, etc.), antibiotics can be used empirically without awaiting definite identification of the causative organism after sending investigations aimed at making a microbiological diagnosis (if available and feasible). Here, CALCA is linked to infection.