In cases of primary pulmonary plague, patients become infected by inhaling bacteria-rich aerosols produced by individuals who developed secondary pneumonia in the course of plague severe blood infection.
Primaarse kopsukatku juhtudel nakatuvad patsiendid baktereid sisaldavate aerosoolide sissehingamisel, mida on eritanud inimesed, kellel on katku ja raske verenakkuse toimel tekkinud teisene kopsupõletik.