Outcomes of Herpes Simplex Virus Pneumonitis in Critically Ill Patients.

Critically ill patients, such as those in intensive care units (ICUs), can develop herpes simplex virus (HSV) pneumonitis. Given the high prevalence of acute respiratory distress syndrome (ARDS) and multiple pre-existing conditions among ICU patients with HSV pneumonitis, factors predicting mortality in this patient population require further investigation. In this retrospective study, the bronchoalveolar lavage or sputum samples of ICU patients were cultured or subjected to a polymerase chain reaction for HSV detection. Univariable and multivariable Cox regressions were conducted for mortality outcomes. The length of hospital stay was plotted against mortality on Kaplan-Meier curves. Among the 119 patients with HSV pneumonitis (age: 65.8 ± 14.9 years), the mortality rate was 61.34% (73 deaths). The mortality rate was significantly lower among patients with diabetes mellitus (odds ratio [OR] 0.12, 95% confidence interval [CI]: 0.02-0.49, p = 0.0009) and significantly higher among patients with ARDS (OR: 4.18, 95% CI: 1.05-17.97, p < 0.0001) or high (≥30) Acute Physiology and Chronic Health Evaluation II scores (OR: 1.08, 95% CI: 1.00-1.18, p = 0.02). Not having diabetes mellitus (DM), developing ARDS, and having a high Acute Physiology and Chronic Health Evaluation II (APACHE II) score were independent predictors of mortality among ICU patients with HSV pneumonitis.

Postpartum Disseminated Herpes Simplex Virus Type 1 Infection With Hemophagocytic Lymphohistiocytosis and Fulminant Neonatal Herpes Infection.

The present study describes a 19-year-old woman with systemic herpes simplex virus (HSV)-1 infection and hemophagocytic lymphohistiocytosis (HLH) postpartum, and a fatal course of neonatal herpesvirus infection. Functional investigation of cells from the mother demonstrated significantly impaired induction of antiviral interferons and cytokines in the context of normal activation of the transcription factors NF-κB and IRF3. Whole-exome sequencing did not reveal any functionally validated genetic variants. We suggest that the functionally impaired antiviral responses, potentially caused by a variant in CASP8 or other variants in noncoding regions of the genome, contributed to the unusually severe disease course observed in two generations.

Distinguishing Features Common to Dual Fatal Herpes Simplex Virus Infections That Occur in Both a Pregnant Woman and Her Newborn Infant.

Deaths from herpes simplex virus type 1 (HSV-1) and herpes simplex virus type 2 (HSV-2) are rare. A major exception is perinatally acquired HSV-1 or HSV-2 infection where the neonatal death rate is substantial. Fatal HSV infection also occurs occasionally in pregnant women. The goal of this review is to enumerate the reports that describe dual deaths of both a pregnant woman and her newborn from a herpesvirus infection. A total of 15 reports were found in the medical literature, of which five described pregnant women with HSV encephalitis and 10 described women with disseminated HSV infection. When the virus was typed, most cases of dual mother/newborn deaths were caused by HSV-2. Of interest, in two situations caused by HSV-1, the pregnant woman probably acquired her primary HSV-1 infection from one of her children and not by sexual transmission. Complete genomic sequencing was performed on one set of HSV-1 isolates collected from mother (blood) and newborn (blood and skin). The mother's strain and the newborn's skin strain were 98.9% identical. When the newborn's two strains were compared, they were 97.4% identical. Only one mother was tested by the HerpeSelect IgG antibody kit. During the nine days of her undiagnosed disseminated infection preceding her death, her serology was negative. In summary, although dual mother/newborn deaths from HSV infection are rare, they continue to be reported as recently as 2017.

Microglia Reduce Herpes Simplex Virus 1 Lethality of Mice with Decreased T Cell and Interferon Responses in Brains.

Herpes simplex virus 1 (HSV-1) infects the majority of the human population and can induce encephalitis, which is the most common cause of sporadic, fatal encephalitis. An increase of microglia is detected in the brains of encephalitis patients. The issues regarding whether and how microglia protect the host and neurons from HSV-1 infection remain elusive. Using a murine infection model, we showed that HSV-1 infection on corneas increased the number of microglia to outnumber those of infiltrating leukocytes (macrophages, neutrophils, and T cells) and enhanced microglia activation in brains. HSV-1 antigens were detected in brain neurons, which were surrounded by microglia. Microglia depletion increased HSV-1 lethality of mice with elevated brain levels of viral loads, infected neurons, neuron loss, CD4 T cells, CD8 T cells, neutrophils, interferon (IFN)-ß, and IFN-γ. In vitro studies demonstrated that microglia from infected mice reduced virus infectivity. Moreover, microglia induced IFN-ß and the signaling pathway of signal transducer and activator of transcription (STAT) 1 to inhibit viral replication and damage of neurons. Our study reveals how microglia protect the host and neurons from HSV-1 infection.

Precision in Cardiovascular Care Using Targeted Neonatal Echocardiography in Lethal Neonatal Disseminated Herpes Infection: A Case Series.

Neonates with disseminated neonatal herpes simplex virus infection often present with cardiorespiratory failure. The pathophysiological contributors to the disease phenotype, biologic mechanisms underlying the hemodynamic instability and optimal approach to cardiovascular treatment have not been well described. We describe clinical and echocardiography features of cardiovascular dysfunction, in a case series of neonates with disseminated herpes simplex virus, and response to physiology-based hemodynamic management. The biologic phenotype includes low systemic vascular resistance state, hypovolemia secondary to third space losses, myocardial dysfunction and pulmonary hypertension. Early targeted neonatal echocardiography provided hemodynamic insights on blood flow, shunt characterization, vascular resistance and cardiac function, that were difficult to gauge clinically (eg, differentiating parenchymal from pulmonary vascular disease) thereby positively impacted clinical care. All patients were stabilized hemodynamically without utilizing extracorporeal membrane oxygenation, although all patients died of multiorgan failure.

Herpes Simplex Virus Infection in Infants: 13 Year Evaluation (2005-2017) of Laboratory Confirmed Cases in Queensland, Australia.

BACKGROUND: National neonatal surveillance for herpes simplex virus (HSV) disease suggests that the incidence of HSV disease may be higher in Queensland (QLD) than in other Australian States. We sought to investigate the incidence via a retrospective 13-year evaluation of statewide laboratory data, autopsy data and linked clinical records of infants with laboratory confirmed infection. METHODS: All positive polymerase chain reaction HSV 1 and 2 results were obtained for infants 0-3 months of age from January 1, 2005 to December 31, 2017. Clinical data were obtained from patient records and parent questionnaires were used to evaluate long-term sequelae. RESULTS: One hundred seventy-two infants with HSV positive polymerase chain reaction results: 121 (70.3%) with HSV 1. Of 104 (60.5%) infants with signs of HSV disease, 76 (73.1%) were neonates (≤28 days of age) [incidence 9.6 (95% confidence interval, 7.0-11.5) per 100,000 live births] and 28 (26.9%) were young infants (29-90 days of age) [3.6 (95% confidence interval, 2.4-5.4) per 100,000 live births]. The annual incidence of neonatal HSV disease increased significantly in Queensland over the study period (P < 0.01). Of the 76 neonates with HSV disease, 58 (76.3%) presented with the skin, eye, mouth (SEM) disease, 17 (22.4%) with HSV encephalitis and 11 (14.5%) had disseminated disease. Young infants presented with HSV skin, eye, mouth disease (21, 75.0%) or HSV encephalitis (6, 21.4%). Death occurred in 12/104 (11.5%) infants (all neonates) with 10 attributable to HSV disease. CONCLUSION: The incidence of neonatal HSV disease in QLD is almost 3 times the national reported incidence. Further research is being undertaken to explore reasons for this change and implications for practice.

Effect of Antiviral Therapy on the Outcome of Mechanically Ventilated Patients With Herpes Simplex Virus Type 1 in BAL Fluid: A Retrospective Cohort Study.

BACKGROUND: Herpes simplex virus type 1 (HSV-1) is frequently detected in the BAL fluid of patients on mechanical ventilation. RESEARCH QUESTION: The aim of the study was to investigate whether antiviral therapy is associated with improved overall survival within 30 days. STUDY DESIGN AND METHODS: This was a retrospective cohort study in four ICUs between January 2011 and December 2017. All adult patients on mechanical ventilation with a respiratory tract infection with positive polymerase chain reaction testing for HSV-1 in the BAL were included. Patients already receiving antiviral agents on the day BAL was performed were excluded. We performed uni- and multivariable Cox and logistic regression modeling. RESULTS: Overall, 306 patients were included in the analysis. Among them, 177 patients (57.8%) received antiviral therapy (90.9% acyclovir, 6.2% ganciclovir, 2.9% both). The overall 30-day mortality rate was 42.4% (n = 75) in the antiviral treatment group and 50.4% (n = 65) in the control group. The adjusted hazard ratio (HR) for the primary outcome was 0.62 (95% CI, 0.44-0.87; P = .005), indicating better overall survival within 30 days for the antiviral-treated group than for the untreated group. This benefit was also present in the subgroup of patients without immunosuppression (n = 246; adjusted HR, 0.53; 95% CI, 0.36-0.78; P = .001). Overall, the median lengths of hospital stay (31 vs 24 days, P = .002) and ICU stay (24 vs 17 days, P < .001), and the duration of mechanical ventilation (18 vs 11 days, P < .001), were longer for patients with therapy. No evidence for the treatment-related deterioration of renal function was observed. INTERPRETATION: These data suggest that detection of HSV-1 in the BAL of patients on mechanical ventilation may be of clinical significance and that specific antiviral treatment may improve clinical outcomes. However, this needs to be proven in multicenter randomized controlled trials before implementation into the clinical routine.

Prognostic factors for survival of herpes simplex virus-associated hemophagocytic lymphohistiocytosis.

Hemophagocytic lymphohistiocytosis (HLH) occurs in neonates with disseminated infection of herpes simplex virus (HSV). Little has been reported on the control of rapid HLH progression. We studied the cytokine profile and genetic basis of two index cases with divergent outcomes after early treatment of type 2 HSV infection. One survivor had fever and elevated serum levels of tumor necrosis factor (TNF)-α, interleukin-6 (IL-6), interferon (IFN)-ß, and IFN-γ at diagnosis. The other neonate had no fever or TNF-α production, but significant IL-6 or IFN responses during the treatment course, and died 19 days after birth. Among 16 reported cases of neonatal HSV-HLH including index cases, eight deceased neonates experienced significantly less fever at presentation (p = 0.028), lower platelet counts (p = 0.019), and lower ratios of soluble IL-2 receptor (sIL-2R) to ferritin levels (p = 0.044) than eight survivors. The 100-day overall survival rates were significantly higher in patients with fever (p = 0.004), > 100 × 109/L of platelet counts (p = 0.035) or > 20 of sIL-2R/ferritin ratio at diagnosis (p = 0.004). The first febrile and cytokine responses to HSV infection predict the early outcome of neonatal HSV-HLH.

Herpes Simplex Infection During Pregnancy, Results of a Tertiary Referral Center in Turkey.

OBJECTIVE: The present study aimed to determine herpes simplex virus (HSV) infection during pregnancy, serologic status of symptomatic patients, and the frequency of PCR and culture positivity and neonatal disease in an obstetric population. MATERIALS AND METHODS: Sera of 1,690 women with genital lesions were tested for HSV IgM and/or HSV IgG between 2008 and 2017. All the patients were evaluated by PCR and viral culture to demonstrate genital herpes infection. RESULTS: The frequency of HSV IgG and IgM seropositivity was 73.8% (1245/1685) and 28.6% (484/1690). The number with a positive viral culture was 288, whereas positive PCR was 305. Five infants had localized skin lesions of HSV infection at the time of birth. CONCLUSION: This study shows the serologic status, viral culture and PCR testing results of pregnant women who had a symptomatic genital HSV infection and efficacy of management strategies to prevent neonatal herpes infection.

Personalized viral genomic investigation of herpes simplex virus 1 perinatal viremic transmission with dual fatality.

Here we present a personalized viral genomics approach to investigating a rare case of perinatal herpes simplex virus 1 (HSV-1) transmission that ended in death of both mother and neonate. We sought to determine whether the virus involved in this rare case had any unusual features that may have contributed to the dire patient outcome. A pregnant woman with negative HerpeSelect antibody test underwent cesarean section at 30 wk gestation and died the same day. The premature newborn died 5 d later. Both individuals were found postmortem to have positive blood HSV-1 PCR tests. Using oligonucleotide enrichment and deep sequencing, we determined that viral transmission from mother to infant was nearly perfect at the consensus genome level. At the virus population level, 77% of minor variants (MVs) in the mother's blood also appeared on the neonate's skin, of which more than half were disseminated into the neonate's blood. We also detected nonmaternal MVs that arose de novo in the neonate's viral populations. Of note, one de novo MV in the neonate's skin virus induced a nonsynonymous mutation in the UL6 protein, which is a component of the portal that allows DNA entry into new progeny capsids. This case suggests that perinatal viremic HSV-1 transmission includes the majority of genetic diversity from the maternal virus population and that new, nonsynonymous mutations can occur after relatively few rounds of replication. This report expands our understanding of viral transmission in humans and may lead to improved diagnostic strategies for neonatal HSV-1 acquisition.

The Absence of Lymphotoxin-α, a Herpesvirus Entry Mediator (HVEM) Ligand, Affects Herpes Simplex Virus 1 Infection In Vivo Differently than the Absence of Other HVEM Cellular Ligands.

Previously, we reported that the absence of herpesvirus entry mediator (HVEM) decreases latency but not primary infection in ocularly infected mice. Recently, we reported that similar to the absence of HVEM, the absence of HVEM ligands (i.e., LIGHT, CD160, and B and T lymphocyte attenuator [BTLA]) also decreased latency but not primary infection. Similar to LIGHT, CD160, and BTLA, another member of tumor necrosis factor (TNF) superfamily, lymphotoxin-α (LTα), also interacts with HVEM. To determine whether LTα decreases latency in infected mice, we ocularly infected LTα-/- mice with latency-associated transcript-positive [LAT(+)] and LAT(-) viruses using similarly infected wild-type (WT) mice as controls. In contrast to WT C57BL/6 mice, LTα-/- mice were highly susceptible to ocular herpes simplex virus 1 (HSV-1) infection, independent of the presence or absence of LAT. Survival was partially restored by adoptive transfer of CD4+, CD8+, or total T cells. Infected LTα-/- mice had significantly higher corneal scarring than WT mice, and adoptive T cell transfer did not alter the severity of eye disease. In contrast to results in WT mice, the amount of latency was not affected by the absence of LAT. The amount of LAT RNA in LTα-/- mice infected with LAT(+) virus was similar to that in WT mice, and adoptive T cell transfer did not alter LAT RNA levels in LTα-/- infected mice. Increased latency in the absence of LTα correlated with upregulation of HVEM, LIGHT, CD160, and BTLA transcripts as well as with an increase in markers of T cell exhaustion. The results of our study suggest that LTα has antipathogenic and anti-inflammatory functions and may act to protect the host from infection.IMPORTANCE Recently, we evaluated the effects of HVEM and its ligands (LIGHT, CD160, and BTLA) on HSV-1 infectivity. However, the effect of LTα, another member of the TNF superfamily, on HSV-1 latency and eye disease is not known. Here, we demonstrate increased latency and corneal scarring in LTα-/- infected mice, independent of the presence of LAT. In addition, infected mice were highly susceptible to HSV-1 infection, and survival was partially but not significantly restored by adoptive T cell transfer. These results suggest that the absence of LTα affects HSV-1 infectivity differently than the absence of HVEM, LIGHT, CD160, and BTLA.

Trends in the incidence, mortality, and cost of neonatal herpes simplex virus hospitalizations in the United States from 2003 to 2014.

OBJECTIVE: To examine the temporal trends in the incidence and outcomes of neonatal herpes simplex infections (NHSV) in the United States. STUDY DESIGN: We conducted a retrospective study using the National Inpatient Sample (NIS). Neonates ≤28 days old with ICD-9 codes for NHSV (054.xx) from 2003 to 2014 were included. Trends in the incidence, mortality, length of stay (LOS), and hospital cost were analyzed using Jonckheere-Terpstra test. RESULTS: NHSV increased from 7.9 to 10 per 100,000 live births from 2003-05 to 2012-14 (P = 0.04). Hospital costs increased from $21,650 to $27,843; P < 0.001). The overall mortality rate and median LOS were 7.9% and 20 days, respectively and there were no significant variations across years during the study period. CONCLUSIONS: The incidence of NHSV in the United States increased between 2003 and 2014 without a significant change in mortality. NHSV remains a serious health threat and new and effective strategies to prevent NHSV are needed.

Infectious causes and outcomes in patients presenting with cerebral spinal fluid pleocytosis.

To evaluate the infectious etiologies, clinical features, and outcomes of patients with CNS infections at a tertiary care center. Patients that present with a pleocytosis in the cerebral spinal fluid (CSF), defined as a CSF WBC count > 5 cells/mm3, from July 2015 to June 2016 at a tertiary care hospital were analyzed for this report. Data from patients with confirmed (n = 43) and presumed (n = 51) CNS infections were analyzed. CNS infection was the leading known cause of CSF pleocytosis (n = 43, 18% of all patients with a pleocytosis in the CSF), and HSV-2 was identified as the leading causative pathogen (n = 10) followed by varicella zoster virus (n = 5). Fifty-three percent of patients with a pleocytosis in the CSF did not receive a diagnosis. In the patients that did not receive a diagnosis, CNS infection was presumed to be the cause in 51 patients (21% of patients with CSF pleocytosis). The mean time to diagnosis for patients with confirmed CNS infection was 16 days, but time to diagnosis was highly variable depending on the causative pathogen. There was a significant overlap in CSF parameters and peripheral white blood cell counts in patients diagnosed with a viral, bacterial, or fungal infection. Neuroimaging changes were present in only 44% of CNS infections. The overall mortality was 7% for CNS infections, and 17% of patients with a CNS infection had a severe neurologic deficit at presentation while only 3% had a severe deficit at the last neurologic assessment. This study provides new insights into the infectious causes of disease in a cohort of patients with pleocytosis in the CSF. The study provides new insights into the time to diagnosis and outcomes in patients that present with pleocytosis in the CSF.

HSV Hepatitis in Pregnancy: A Review of the Literature.

IMPORTANCE: Herpes simplex virus (HSV) hepatitis is a rare condition with a high mortality rate. Immunocompromised individuals, including pregnant women, are the most susceptible. When primary infection occurs during pregnancy, risk for disseminated HSV is greatly increased. Disseminated HSV can manifest in the form of HSV hepatitis. OBJECTIVE: We aim to review the literature and summarize what is known about HSV hepatitis in pregnancy to aid in the diagnosis and treatment of this condition. EVIDENCE ACQUISITION: A literature search of PubMed and Web of Science was performed. A total of 237 citations were found. All citations were independently reviewed. Thirty-eight full-text articles were identified and included in this review. Additional data from 1 unpublished case from our institution was included. RESULTS: Fifty-six cases were included with average gestational age at diagnosis of 30 weeks. Patients presented with a wide variety of gastrointestinal, respiratory, neurologic, and urogenital symptoms. The most common examination findings were fever and abdominal tenderness. Only 18.2% of patients had a vesicular rash. All patients had a transaminitis, and 85% had positive viral cultures. A multitude of treatments were used with the majority of favorable outcomes occurring after treatment with acyclovir. CONCLUSIONS AND RELEVANCE: Although HSV hepatitis is rare, it carries a mortality rate of up to 39% for mothers and neonates. Therefore, it is crucial that HSV hepatitis be included on the differential diagnosis when a patient presents with fever and transaminitis. When HSV hepatitis is suspected, empiric therapy with acyclovir can be initiated with no additional risk to the fetus.

IL-17A contributes to HSV1 infection-induced acute lung injury in a mouse model of pulmonary fibrosis.

BACKGROUND: Patients with idiopathic pulmonary fibrosis (IPF) often experience acute exacerbation (AE) after an episode of common cold. AIMS: To establish a mouse model of virus infection-induced AE-IPF and investigate the mechanism underlying the AE-IPF. METHODS: Herpes simplex virus 1 (HSV1) was inoculated intranasally to wild-type (WT) and IL-17A gene knockout (IL-17A-/- ) mice 21 days after intratracheal administration of bleomycin (BLM). RESULTS: HSV1 infection caused acute exacerbation in mice with BLM-induced fibrosis. Compared with the BLM+Saline mice, the mice with BLM+HSV1 showed significantly higher acute lung injury (ALI) score (P < 0.0001), lower survival rate (100% vs 21.4%, P < 0.0001), poorer lung function and higher inflammatory response representing by increased total inflammatory cells in bronchoalveolar lavage fluid (BALF) (P = 0.0323), increased proportion of Th17 cells in peripheral blood (P = 0.0004) and higher inflammatory factors in BALF. In addition, HSV1 infection increased the expression of endoplasmic reticulum stress (ERS)-related proteins in mice with BLM-induced fibrosis. The inhibition of ERS by tauroursodeoxycholic acid (TUDCA, an ERS inhibitor) significantly reduced the IL-17A levels in BALF (P = 0.0140) and TH17 cells in the peripheral blood (P = 0.0084) of mice with BLM+HSV1, suggesting that suppression of ERS may reduce TH17 response in mice with AE-IPF. Compared with WT mice with BLM+HSV1, IL-17A-/- mice with BLM+HSV1 had lower ALI score (P = 0.0119), higher survival rate (78.6% vs 21.4%, P = 0.004), improved lung function, and milder inflammatory response. CONCLUSIONS: HSV1 infection in addition to BLM-induced IPF can successfully establish AE-IPF in mice. IL-17A and ERS promote lung inflammation in AE-IPF development.

[Ophthalmic drug films in the therapy of experimental herpetic keratoconjunctivitis.]

INTRODUCTION: The complexity of the treatment of herpetic keratoconjunctivitis is due to the severity of the disease, complications, the transition to chronic relapsing forms and the insufficient effectiveness of the drugs used, which leads to a steady increase in the number of patients. The aim of the study was to evaluate the therapeutic efficacy of the eye drug films «GlazAvir¼ in the experimental model of acute herpetic eye infection in rabbits. RESEARCH OBJECTIVES: to study the specific activity of «GlazAvir¼ and compare the long-term indicators of the level of manifestation of individual clinical signs of keratoconjunctivitis. MATERIAL AND METHODS: In the work we used rabbits of the Chinchilla breed, the herpes simplex virus type 1 and the eye drug films «GlazAvir¼. A model of ophthalmic herpetic infection was formed by infection of rabbits with virus-containing material of a pre-scarified eye cornea against the background of local anesthesia. Аnimals were treated with the drug «GlazAvir¼ - 1 application per day for 7 days. Animals were observed daily for 15 days, then every 3 days until the 25th day of observation. The effectiveness of the drug was evaluated at the peak of the development of the pathological process. RESULTS AND DISCUSSION: There was a decrease in mortality from 50 to 20%, and an increase in average life expectancy by 27.87%, compared with the control in animals treated with «GlazAvir¼. It was noted after activation of herpetic keratoconjunctivitis on the 2nd - 5th day, at the peak of the disease (6-9th day) a statistically significant decrease in the activity of the pathological process (p<0.05) by rabbits treated with the «GlazAvir¼ ophthalmic drug films. The tendency to normalization by the rabbits treated with the «GlazAvir¼ preparation was observed until the 14th day. CONCLUSION: The data obtained indicate the pronounced effectiveness of the «GlazAvir¼ preparation in the treatment of experimental herpesvirus keratoconjunctivitis.

Topical treatment of herpes simplex virus infection with enzymatically created siRNA swarm.

BACKGROUND: Herpes simplex virus (HSV) is a common human pathogen. Despite current antivirals, it causes a significant medical burden. Drug resistant strains exist and they are especially prevalent in immunocompromised patients and in HSV eye infections. New treatment modalities are needed. METHODS: BALB/c mice were corneally infected with HSV and subsequently treated with a swarm of enzymatically created, Dicer-substrate small interfering RNA (siRNA) molecules that targeted the HSV gene UL29. Two infection models were used, one in which the infection was predominantly peripheral and another in which it spread to the central nervous system. Mouse survival, as well as viral spread, load, latency and peripheral shedding, was studied. RESULTS: The anti-HSV-UL29 siRNA swarm alleviated HSV infection symptoms, inhibited viral shedding and replication and had a favourable effect on mouse survival. CONCLUSIONS: Treatment with anti-HSV-UL29 siRNA swarm reduced symptoms and viral spread in HSV infection of mice and also inhibited local viral replication in mouse corneas.

Incidence and mortality of herpes simplex encephalitis in Denmark: A nationwide registry-based cohort study.

OBJECTIVES: We aimed to investigate the incidence and mortality of herpes simplex encephalitis (HSE) in a nationwide cohort. METHODS: From the Danish National Patient Registry, we identified all adults hospitalised with a first-time diagnosis of HSE in Denmark during 2004-2014. The HSE diagnoses were verified using medical records and microbiological data. Patients were followed for mortality through the Danish Civil Registry System. We estimated age-standardised incidence rates of HSE and 30-day, 60-day, and 1-year cumulative mortality. Furthermore, we assessed whether calendar year, age, gender, level of comorbidity, virus type, and department type was associated with HSE mortality. RESULTS: We identified a total of 230 cases of HSE. Median age was 60.7 years (interquartile range: 49.3-71.6). The overall incidence rate was 4.64 cases per million population per year (95% confidence interval: 4.06-5.28). The cumulative mortality within 30 days, 60 days, and 1 year of the HSE admission was 8.3%, 11.3%, and 18.6%, respectively. Advanced age and presence of comorbidity were associated with increased 60-day and 1-year mortality. CONCLUSIONS: This nationwide study of verified HSE found a higher incidence than reported in previous nationwide studies. Presence of comorbidity was identified as a novel adverse prognostic factor. Mortality rates following HSE remain high.