The Cytopathology of Infectious Disease: A Review

Infectious diseases continue to represent a major global burden, remaining among the leading causes of morbidity and mortality. Cytopathology is a valuable diagnostic tool across diverse healthcare settings, including both high-income and low- and middle-income countries for diagnosis of infection. Its cost-effectiveness and ability to provide rapid results make it particularly well suited for timely clinical decision-making, which can be critical and, in some cases, lifesaving in a patient with an infectious disease. While cytopathology often yields sufficient information for diagnosis, confirmatory ancillary techniques, such as microbiological studies, immunocytochemistry, and molecular assays, may be necessary in selected cases to establish a definitive diagnosis.

The practicing cytopathologist and cytologist must be familiar with the cytomorphologic diagnosis of infection. This review article highlights the cytomorphologic features of infectious diseases that can be diagnosed cytologically, the utility of ancillary tests, and discusses both the advantages and limitations of cytopathology in this context.

Careful and systematic attention to cytomorphologic features, including both the infectious agents and the characterisation of the host tissue response, together with clinicoradiologic correlation and the judicious application of ancillary diagnostic tests, is essential for achieving an accurate diagnosis of infection. Such an integrated approach minimises the risk of false-negative and false-positive interpretations, ensures specimens are appropriately classified within the correct cytologic reporting category, and facilitates informed decisions regarding the selection of ancillary investigations.