A method for determining a patient's susceptibility of contracting a nosocomial infection that includes obtaining a biological sample from the patient and extracting biological material from the biological sample; preparing a specific reagent of an expression product of at least one target gene selected from S100A9 and S100A8 target genes; and determining the expression of at least one of the target genes S100A9 and S100A8, where overexpression relative to a specified threshold value indicates susceptibility of contracting a nosocomial infection.