[ \textbf{CLABSI rate} = \left(\frac{\text{Number of CLABSI events in the period}}{\text{Total central-line days in the same period}}\right) \times 1000 ]

Reported as CLABSIs per 1,000 central-line days. This is the CDC/NHSN surveillance calculation. CDC NHSN manual

[ \left(\frac{3}{1250}\right) \times 1000 = 2.4 ]

Central-line days means the daily total number of patients with one or more eligible central lines. A patient with two central lines on one day still contributes one central-line day.

Related measure:

[ \textbf{Central-line utilization ratio} = \frac{\text{Central-line days}}{\text{Patient-days}} ]

Use the relevant surveillance definition for what counts as a CLABSI, rather than assuming every bloodstream infection in a patient with a central line is line-associated. A CLABSI is a laboratory-confirmed bloodstream infection in a patient with a qualifying central line and no other identified source. Fischer's Mastery of Surgery - 8th e, lines 3419-3427.