1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 AbstractThe significance of detection of herpes viruses in respiratory secretions of critically ill patients is controversial. The study aim was to determine the prevalence of herpes virus DNA in respiratory secretions in patients on artificial ventilation. Respiratory secretions taken thrice weekly from 174 patients in a tertiary centre Intensive Therapy Unit (ITU) were tested for Herpes Simplex Virus (HSV) by nested PCR. Samples from 61 patients in ITU for 4 days or more were also tested for Epstein Barr Virus (EBV) and Cytomegalovirus (CMV) using real-time PCR.HSV positivity increased with ITU stay with 18.6% admission samples positive, 32.5 % day 2-5 samples, and 65.9% day 6-39 samples. Being HSV positive on admission did not influence mortality (9/27, 33.3% v 38/118, 32.2%) however, subsequently, mortality of those negative but becoming positive was higher than in those remaining negative (10/35, 29% v 5/24 21%). At least one sample was EBV positive in 61% and CMV positive in 19% of patients tested. Of 63 patients tested for all three viruses, 4 were positive for three viruses, 23 patients for two viruses, 24 for one virus and 12 were negative for all the above viruses.Detection of HSV, EBV and CMV is common in ITU patients. Becoming HSV positive while in ITU may increase mortality. Word count 204