Welcome or not Herpes Simplex virus (HSV) is an ever present guest in the intensive care unit (ICU). Several studies have documented a high frequency of HSV reactivation in critically ill patients despite that clinical impact remains unknown.

Normally primary HSV infection is asymptomatic but can under certain circumstances cause manifestations such as encephalitis and bronchopneumonitis. Bruynseels showed that HSV was detectable in the throat of two percent of healthy volunteers and three percent of patients not admitted to the ICU, this provides a broad "recruitment-base" for either latent or lytic HSV infection in the ICU. Viral dissemination to the bloodstream is seen in neonates , immunocompromised patients, but also in patients with primary herpetic gingivostomatitis. Patients testing polymerase chain reaction (PCR) positive for herpes simplex DNA in blood, have a higher rate of systemic symptoms than those testing PCR negative for herpes simplex. Additionally it is known that HSV suppression in HIV patients has beneficial effects. PCR, now being available for more than a decade, has been shown to provide a more sensitive method for the detection of HSV than culture, but viral detection does not per se translate to viral disease thus the impact of disseminated HSV infection in ICU patients remains unclear.

The investigators would like to investigate the incidence of HSV reactivation in blood and tracheal secretions critically ill patients and its impact on clinical course.

Inclusion Criteria:

• Admission to ICU
• Expected length of stay (LOS) >72 hours
• Intubated <24 hours prior to inclusion
• Informed consent by patient, relative or guardian

Exclusion Criteria:

• Ongoing antiviral treatment/prophylaxis
• Expected LOS <72 hours
• Intubation >24 hours prior to inclusion
• Withdrawal of informed consent

Adult critically ill patients