Systemic infection and microglia activation: a prospective postmortem study in sepsis patients.

BACKGROUND: Systemic infection is associated with long-term cognitive deficits and functional decline. In this study we hypothesized that severe systemic inflammation leads to a neuroinflammatory response that is characterized by microglial activation, and that these effects might be more pronounced in patients using medication with anticholinergic side-effects. METHODS: Based on the results of a pilot study in 8 patients, we assessed the number of MHC-II and CD-68 positive cells by immunohistochemistry and compared the number of microglia in specific brain regions of 16 well-characterized patients with septic shock and 15 controls. RESULTS: In the pilot study, patients with sepsis tended to have higher density of MHC-II and CD-68 positive microglia in the basal ganglia (putamen, caudate nucleus and globus pallidus) and of MHC-II positive microglia in the hippocampus. In the validation study, patients with sepsis had a significantly higher number of CD-68 positive cells in hippocampus (1.5 fold; p = 0.012), putamen (2.2 fold; p = 0.008) and cerebellum (2.5 fold; p = 0.011) than control patients. The density of MHC-II positive microglia was similar between sepsis and control groups. There was no consistent correlation between microglia counts and anti-cholinergic activity drugs score. CONCLUSION: In patients who die during septic shock, severe systemic inflammation is accompanied by localized and strong upregulation of CD-68 positive microglia, but not of MHC-II positive microglia. We identified regional differences in the brain with increased microglial activation in putamen, hippocampus and cerebellum.

Clinical and Laboratory Characteristics for the Diagnosis of Bacterial Ventriculitis After Aneurysmal Subarachnoid Hemorrhage.

BACKGROUND: The diagnosis of nosocomial bacterial ventriculitis in patients with subarachnoid hemorrhage (SAH) can be challenging. METHODS: We performed a retrospective study on the diagnostic accuracy of clinical and laboratory characteristics for the diagnosis of bacterial ventriculitis in 209 consecutive patients with an aneurysmal SAH admitted in a tertiary referral center from 2008 to 2010. Diagnostic value of clinical characteristics and inflammatory indexes in CSF and blood were determined for three diagnostic categories: (1) no suspicion for bacterial ventriculitis; (2) clinical suspicion for bacterial ventriculitis, defined as initiation of empirical antibiotic treatment for ventriculitis, but negative CSF cultures; and (3) CSF culture-positive bacterial ventriculitis. RESULTS: Empirical antibiotics for suspected ventriculitis was initiated in 48 of 209 (23 %) patients. CSF cultures were positive in 11 (5 %) patients. Within the group of suspected ventriculitis, only longer duration of CSF drainage and lower CSF red blood cell counts predicted for culture positivity. None of the other clinical features or inflammatory indexes in CSF and blood were associated with culture-proven bacterial ventriculitis. CONCLUSIONS: Nosocomial bacterial ventriculitis in patients with aneurysmal SAH is often suspected but confirmed by culture in a minority of cases. Improvement of diagnostics for nosocomial bacterial ventriculitis in patients with aneurysmal SAH is needed.

Help seeking behavior and onset-to-alarm time in patients with acute stroke: sub-study of the preventive antibiotics in stroke study.

BACKGROUND: Patients with acute stroke often do not seek immediate medical help, which is assumed to be driven by lack of knowledge of stroke symptoms. We explored the process of help seeking behavior in patients with acute stroke, evaluating knowledge about stroke symptoms, socio-demographic and clinical characteristics, and onset-to-alarm time (OAT). METHODS: In a sub-study of the Preventive Antibiotics in Stroke Study (PASS), 161 acute stroke patients were prospectively included in 3 Dutch hospitals. A semi-structured questionnaire was used to assess knowledge, recognition and interpretation of stroke symptoms. With in-depth interviews, response actions and reasons were explored. OAT was recorded and associations with socio-demographic, clinical parameters were assessed. RESULTS: Knowledge about stroke symptoms does not always result in correct recognition of own stroke symptoms, neither into correct interpretation of the situation and subsequent action. In our study population of 161 patients with acute stroke, median OAT was 30 min (interquartile range [IQR] 10-150 min). Recognition of one-sided weakness and/or sensory loss (p = 0.046) and adequate interpretation of the stroke situation (p = 0.003), stroke at daytime (p = 0.002), severe stroke (p = 0.003), calling the emergency telephone number (p = 0.004), and transport by ambulance (p = 0.040) were associated with shorter OAT. CONCLUSION: Help seeking behavior after acute stroke is a complex process. A shorter OAT after stroke is associated with correct recognition of one-sided weakness and/or sensory loss, adequate interpretation of the stroke situation by the patient and stroke characteristics and logistics of stroke care, but not by knowledge of stroke symptoms.

Bacterial meningitis in solid organ transplant recipients: a population-based prospective study.

BACKGROUND: Solid organ transplant (SOT) recipients are at risk of infections of the central nervous system. However, the incidence and clinical course of bacterial meningitis in SOT recipients are unclear. We studied occurrence, disease course, and prognosis of bacterial meningitis in SOT recipients in the Netherlands. METHODS: All patients with a medical history of solid organ transplantation were selected from our nationwide prospective cohort study on community-acquired bacterial meningitis in patients >16 years old, performed from March 1, 2006 to October 31, 2014. Data on patient history, symptoms and signs on admission, treatment, and outcome were collected prospectively. For transplant recipients, additional information was collected retrospectively. RESULTS: We identified 6 SOT recipients, all receiving renal transplants. The annual incidence of bacterial meningitis was 7-fold higher (95% confidence interval [CI] 2.94-17.02, P < 0.001) for renal transplant recipients as compared with the general population (9.56 [95% CI 3.98-22.96] vs. 1.35 [95% CI 1.28-1.43] per 100,000 patients per year). One of the 6 patients (17%) presented with the classic presentation of bacterial meningitis (fever, neck stiffness, and change in mental status). Seizures were common, occurring in 33% of patients. Streptococcus pneumoniae and Listeria monocytogenes were identified in 2 patients each, and Escherichia coli and Pseudomonas aeruginosa were both identified once. Four of 6 patients (67%) had an unfavorable functional outcome. CONCLUSION: Bacterial meningitis is a rare but devastating complication of solid organ transplantation. SOT recipients are at high risk for developing meningitis, and recognition of this condition may be difficult, owing to atypical clinical manifestation.

Eosinophilia à deux: a brain nagging souvenir from the Philippines.

Angiostrongylus cantonensis is the most common cause of eosinophilic meningitis. Although a rare condition among travelers, increased travel and global transportation of food products may result in more cases across non-endemic, developed countries in the future. We here describe two men with headache and painful skin after visiting the Philippines as presenting symptoms. Subsequently, confusion and focal neurologic symptoms developed. Both had increased serum eosinophils; however, CSF eosinophilia was only demonstrated after repeated lumbar puncture. In the CSF of both, Angiostrongylus spp. DNA was detected. Both were treated with albendazole combined with corticosteroids, after which symptoms improved.

Diagnostic accuracy of clinical and laboratory characteristics in suspected non-surgical nosocomial central nervous system infections.

BACKGROUND: The diagnosis of meningitis in non-surgical hospitalized patients is often difficult and diagnostic accuracy of clinical, laboratory, and radiological characteristics is unknown. AIM: To assess diagnostic accuracy for individual clinical characteristics of patients suspected of non-surgical nosocomial central nervous system (CNS) infections. METHODS: In a prospective multi-centre cohort study in the Netherlands with adults suspected of CNS infections, consecutive patients who underwent a lumbar puncture for the suspicion of a non-surgical nosocomial CNS infection were included. All episodes were categorized into five final clinical diagnosis categories, as reference standard: CNS infection, CNS inflammatory disease, systemic infection, other neurological disease, or non-systemic, non-neurological disease. FINDINGS: Between 2012 and 2022, 114 out of 1275 (9%) patients included in the cohort had suspected non-surgical nosocomial CNS infection: 16 (14%) had a confirmed diagnosis, including four (25%) with bacterial meningitis, nine (56%) with viral CNS infections, two (13%) fungal meningitis, and one (6%) parasitic meningitis. Diagnostic accuracy of individual clinical characteristics was generally low. Elevated CSF leucocyte count had the highest sensitivity (81%; 95% confidence interval (CI): 54-96) and negative predictive value (NPV) (96%; 95% CI: 90-99). When combining the presence of abnormalities in neurological or CSF examination, sensitivity for diagnosing a CNS infection was 100% (95% CI: 79-100) and NPV 100% (95% CI: 78-100). CSF examination changed clinical management in 47% of patients. CONCLUSION: Diagnostic accuracy for individual clinical characteristics was low, with elevated CSF leucocyte count having the highest sensitivity and NPV.

The course of post-stroke apathy in relation to cognitive functioning: a prospective longitudinal cohort study.

Apathy is common after stroke and has been associated with cognitive impairment. However, causality between post-stroke apathy and cognitive impairment remains unclear. We assessed the course of apathy in relation to changes in cognitive functioning in stroke survivors. Using the Apathy Scale (AS) and cognitive tests on memory, processing speed and executive functioning at six- and 15 months post-stroke we tested for associations between (1) AS-scores and (change in) cognitive scores; (2) apathy course (persistent/incident/resolved) and cognitive change scores. Of 117 included participants, 29% had persistent apathy, 13% apathy resolving over time and 10% apathy emerging between 6-15 months post-stroke. Higher AS-scores were cross-sectionally and longitudinally associated with lower cognitive scores. Relations between apathy and cognitive change scores were ambiguous. These inconsistent relations between apathy and changes in cognition over time suggest that post-stroke apathy does not directly impact cognitive performance. Both these sequelae of stroke require separate attention.

[Bacterial meningitis]. / Bacteriële meningitis.

Bacterial meningitis is a severe disease which affects 35.000 Europeans each year and has a mortality rate of about 20%. During the past 25 years the epidemiology of bacterial meningitis has changed significantly due to the implementation of vaccination against Haemophilus influenzae, Neisseria meningtidis group C and Streptococcus pneumoniae. Due to these vaccines, meningitis is now predominantly a disease occurring in adults, caused especially by Streptococcus pneumoniae, while it was formerly a child disease which was largely caused by Haemophilus influenzae. Bacterial meningitis is often difficult to recognize since the classical presentation with neck stiffness, reduced awareness and fever occurs in less than half of the patients. The only way to diagnose or exclude bacterial meningitis is by performing low-threshold cerebrospinal fluid examination with a suspicion of bacterial meningitis. The treatment consists of the prescription of antibiotics and dexamethasone.

Genome sequence of Neisseria meningitidis serogroup B strain H44/76.

Neisseria meningitidis is an obligate human pathogen. While it is a frequent commensal of the upper respiratory tract, in some individuals the bacterium spreads to the bloodstream, causing meningitis and/or sepsis, which are serious conditions with high morbidity and mortality. Here we report the availability of the genome sequence of the widely used serogroup B laboratory strain H44/76.

Diagnostic accuracy of VIDISCA-NGS in patients with suspected central nervous system infections.

OBJECTIVES: Confirming the diagnosis in viral central nervous system (CNS) infections can be difficult with the currently available diagnostic tools. Virus discovery cDNA-amplified fragment length polymorphism next-generation sequencing (VIDISCA-NGS) is a promising viral metagenomic technique that enables the detection of all viruses in a single assay. We performed a retrospective study on the diagnostic accuracy of VIDISCA-NGS in cerebrospinal fluid (CSF) of individuals with suspected CNS infections. METHODS: Consecutive adult patients presenting to the Emergency Department or inpatients, who underwent a lumbar puncture for the suspicion of a CNS infection, were included if they were diagnosed with a viral CNS infection, or if a viral CNS infection was initially suspected but eventually a different diagnosis was made. A quantitative PCR panel of the most common causative viruses was performed on CSF of these patients as reference standard and compared with the results of VIDISCA-NGS, the index test. RESULTS: We included 38 individuals with viral CNS infections and 35 presenting with suspected CNS infection for whom an alternative aetiology was finally established. Overall sensitivity and specificity were 52% (95% CI 31%-73%) and 100% (95% CI 91%-100%), respectively. One enterovirus, detected by VIDISCA-NGS, was only identified by quantitative PCR upon retesting. Additional viruses identified by VIDISCA-NGS consisted of GB virus C, human papillomavirus, human mastadenovirus C, Merkel cell polyoma virus and anelloviruses. CONCLUSION: In patients for whom routine diagnostics do not yield a causative pathogen, VIDISCA-NGS can be of additional value as it can detect a broader range of viruses, but it does not perform well enough to replace quantitativePCR.

Impact of the COVID-19 outbreak on acute stroke care.

BACKGROUND AND PURPOSE: There are concerns that the coronavirus disease 2019 (COVID-19) outbreak negatively affects the quality of care for acute cardiovascular conditions. We assessed the impact of the COVID-19 outbreak on trends in hospital admissions and workflow parameters of acute stroke care in Amsterdam, The Netherlands. METHODS: We used data from the three hospitals that provide acute stroke care for the Amsterdam region. We compared two 7-week periods: one during the peak of the COVID-19 outbreak (March 16th-May 3th 2020) and one prior to the outbreak (October 21st-December 8th 2019). We included consecutive patients who presented to the emergency departments with a suspected stroke and assessed the change in number of patients as an incidence-rate ratio (IRR) using a Poisson regression analysis. Other outcomes were the IRR for stroke subtypes, change in use of reperfusion therapy, treatment times, and in-hospital complications. RESULTS: During the COVID-19 period, 309 patients presented with a suspected stroke compared to 407 patients in the pre-COVID-19 period (IRR 0.76 95%CI 0.65-0.88). The proportion of men was higher during the COVID-19 period (59% vs. 47%, p < 0.001). There was no change in the proportion of stroke patients treated with intravenous thrombolysis (28% vs. 30%, p = 0.58) or endovascular thrombectomy (11% vs 12%, p = 0.82) or associated treatment times. Seven patients (all ischemic strokes) were diagnosed with COVID-19. CONCLUSION: We observed a 24% decrease in suspected stroke presentations during the COVID-19 outbreak, but no evidence for a decrease in quality of acute stroke care.

Neurological complications following adult lung transplantation.

The full spectrum of neurologic complications and their impact on survival in lung recipients has not been reported. A retrospective cohort review of the Mayo Clinic Lung Transplant Registry (1988-2008) was performed to determine the range of neurologic complications in a cohort of adult lung recipients. Cox regression models were used to assess risk factors for neurological complications and death posttransplant. One hundred and twenty lung transplant recipients (53% women, median age at transplantation 53 years, range 21-73, median survival 4.8 years) were identified, of whom 95 had a neurological complication posttransplantation (median time to complication 0.8 years). Neurological complications were severe in 46 patients (requiring hospitalization or urgent care and evaluation) and were most often perioperative stroke or encephalopathy. Age predicted neurological complications of any type, whereas lung allocation score, bilateral lung transplantation, sex, underlying lung disease, elevated hemoglobin A1C, renal insufficiency and smoking history did not. Neurological complications of any severity (HR 4.3, 95% CI 2.2-8.6, p < 0.001) and high severity (HR 7.2, 95% CI 3.5-14.6, p < 0.001) were associated with increased risk of death. Neurological complications are common after lung transplantation, affecting 92% of recipients within 10 years. Severe neurologic complications are also common, affecting 53% of recipients within 10 years.

Resurgence of pneumococcal meningitis in Europe and Northern America.

BACKGROUND: Streptococcus pneumoniae is the most common pathogen causing bacterial meningitis. The routine use of multivalent conjugate pneumococcal vaccines has led to a decline of invasive pneumococcal disease caused by serotypes included in the vaccine serotypes. Recently, several reports have described a concomitant rise in the incidence of non-vaccine serotypes, suggesting serotype replacement. OBJECTIVE: We aim to review the effect of pneumococcal vaccination on the incidence of pneumococcal meningitis in Europe and northern America with a particular interest in serotype replacement. SOURCES: Articles that include data on invasive pneumococcal disease incidence before and after the introduction of vaccination, or on invasive pneumococcal serotype, are discussed, with a focus on pneumococcal meningitis. CONTENT: The introduction of pneumococcal conjugate vaccines has universally resulted in a decline in vaccine-serotype pneumococcal meningitis incidence throughout Europe and northern America. Serotype replacement by non-vaccine serotypes has however been reported following the introduction of the 7-, 10- and 13-valent pneumococcal conjugate vaccines, which in several regions abolished the overall effect of vaccination on pneumococcal meningitis incidence. IMPLICATIONS: The promising decline in the incidence of pneumococcal meningitis following the introduction of vaccination seems to have been temporary. Replacement by non-vaccine serotypes illustrates that pneumococcal meningitis continues to pose a major challenge. We need new approaches to prevention, new vaccines and continued efforts to improve treatment for patients with pneumococcal meningitis.

Incidence and mortality of brain abscess in Denmark: a nationwide population-based study.

OBJECTIVES: To examine the incidence and mortality of brain abscesses. METHODS: We accessed nationwide population-based medical registries to obtain data for patients with first-time brain abscesses in Denmark from 1982 through 2016. Annual age- and sex-standardized incidence rates with 95% confidence intervals were calculated and compared by direct standardization. We used Cox regression to compute mortality rate ratios adjusted for age and year groups, sex and Charlson comorbidity index score. RESULTS: We identified 1384 patients (37% female). The overall standardized incidence rate of brain abscess was 0.76 per 100 000 person-years (95% confidence interval 0.70-0.81). The incidence rates gradually increased from 0.60 during 1982-88 to 0.90 per 100 000 person-years during 2010-16, yielding an incidence rate ratio of 1.50 (95% confidence interval 1.26-1.79). This increase in incidence was most pronounced in the proportions of brain abscess patients >40 years of age and those with immuno-compromise. The 1-year mortality declined from 29% during 1982-88 to 20% during 2010-16, yielding an adjusted mortality rate ratio of 0.44 (95% confidence interval 0.31-0.63). Risk factors for death were advanced age, Charlson comorbidity index >0, immuno-compromised status and congenital heart disease. CONCLUSIONS: The incidence of brain abscess in Denmark is low but increasing, especially in the elderly, along with an increasing proportion of brain abscess patients with immuno-compromise. The prognosis has improved during the last decades, but mortality remains high. Risk factors for death in our study were advanced age, presence of comorbidity, immuno-compromised status and congenital heart disease.

Community-acquired pneumonia in patients with bacterial meningitis: a prospective nationwide cohort study.

OBJECTIVE: Pneumonia is considered a focus of infection in patients presenting with community-acquired bacterial meningitis but the impact on disease course is unclear. The aim was to study presenting characteristics, clinical course and outcome of meningitis patients with co-existing pneumonia on admission. METHODS: We evaluated adult patients with community-acquired bacterial meningitis with pneumonia on admission in a nationwide, prospective cohort performed from March 2006 to June 2017. We performed logistic regression analysis to identify clinical characteristics predictive of pneumonia on admission, and to quantify the effect of pneumonia on outcome. RESULTS: Pneumonia was diagnosed on admission in 315 of 1852 (17%) bacterial meningitis episodes and confirmed by chest X-ray in 256 of 308 (83%) episodes. Streptococcus pneumoniae was the causative organism in 256 of 315 episodes (81%). Pneumonia on admission was associated with advanced age (OR 1.03 per year increase, 95% CI 1.02-1.04, p < 0.001), alcoholism (OR 1.96, 95% CI 1.23-3.14, p 0.004), cancer (OR 1.54, 95% CI 1.12-2.13, p 0.008), absence of otitis or sinusitis (OR 0.44, 95% CI 0.32-0.59, p < 0.001) and S. pneumoniae (OR 2.14, 95% CI 1.55-2.95, p < 0.001) in the multivariate analysis. An unfavourable outcome defined as a score of 1-4 on the Glasgow Outcome Scale was observed in 172 (55%) episodes and 87 patients (28%) died. Pneumonia on admission was independently associated with unfavourable outcome and mortality in the multivariate analysis (OR 1.48, 95% CI 1.12-1.96; p 0.005). CONCLUSION: Pneumonia on admission in bacterial meningitis is a frequent coexisting infection and is independently associated with unfavourable outcome and mortality.

Long-term neurologic and cognitive outcome and quality of life in adults after pneumococcal meningitis.

OBJECTIVES: To perform a cross-sectional cohort study on long-term neurologic, cognitive and quality-of-life outcome in adults surviving pneumococcal meningitis. METHODS: Adult survivors of community-acquired pneumococcal meningitis from a Dutch nationwide prospective cohort study were evaluated 1 to 5 years after acute illness. The control group consisted of partners or proxies of patients. Neurologic examination was performed and cognitive domains were tested with the Vienna Test System Cognitive Basic Assessment Test set (VTS COGBAT). The Research and Development (RAND)-36 and adapted Cognitive and Emotional Consequences of Stroke (CLCE)-24 questionnaires assessed perceived cognitive functioning and quality of life. Differences between group scores were tested with multivariate analyses of variance. RESULTS: A total of 80 pneumococcal meningitis patients and 69 controls were evaluated. After a median of 2 years (interquartile range, 2-3) after acute illness, 27 (34%) of 79 patients had persistent neurologic sequelae, most commonly hearing loss (21/79, 27%). On overall neuropsychologic evaluation, patients performed worse than the controls (MANCOVA; p 0.008), with alertness (z score -0.33, p 0.011) and cognitive flexibility (z score -0.33, p 0.027) as the most affected domains. Cognitive impairment was present in 11 (14%) of 79 patients. CLCE-24 questionnaires revealed cognitive impairment on all domains, most commonly for cognitive speed (53/75, 71%), attention (45/75, 60%) and memory (46/75, 61%). Patients had lower quality-of-life scores than controls (item physical functioning, (median) patients vs. controls, 80 vs. 95, p < 0.001; social functioning, (median) 81 vs. 100, p 0.003; perceived health, (mean) 59 vs. 70, p 0.005), which correlated with cognitive complaints (R = 0.66, p < 0.001). CONCLUSIONS: Adults after pneumococcal meningitis are at high risk of long-term neurologic and neuropsychologic deficits impairing daily life activities and quality of life.

Corticosteroids for acute adult bacterial meningitis.

Bacterial meningitis in adults is a severe disease, with high fatality and morbidity rates. Experimental studies showed that the inflammatory response in the subarachnoid space is associated with unfavorable outcome. In these experiments, corticosteroids, and in particular dexamethasone, were able to reduce the inflammatory cascades in the subarachnoid space. The use of corticosteroids as adjunctive therapy in adults with bacterial meningitis was evaluated in eight studies, performed over 45 years. Most studies on adjunctive dexamethasone therapy in adults with bacterial meningitis suffered from methodological flaws. In 2002, a trial with sufficient study-power to show significant differences was published. This study showed that adjunctive dexamethasone therapy reduced the rate of unfavorable outcomes from 25 to 15% in adults with bacterial meningitis. In this study, adjunctive treatment with dexamethasone was given before or with the first dose of antibiotics, without serious adverse effects. A quantitative review showed a consistent beneficial effect of dexamethasone on mortality and a borderline statistical beneficial effect on neurologic sequels. On the basis of available evidence, adjunctive dexamethasone therapy should be initiated before or with the first dose of antibiotics and continued for four days in all adults with suspected or proven community bacterial meningitis in high-income countries, regardless of bacterial etiology. Since prompt use of dexamethasone and appropriate antibiotics improves the prognosis of adults with bacterial meningitis, hospitals will need protocols to include dexamethasone with the initial antibiotic therapy.

Variation in coagulation and fibrinolysis genes evaluated for their contribution to cerebrovascular complications in adults with bacterial meningitis in the Netherlands.

OBJECTIVE: To study whether genetic variation in coagulation and fibrinolysis genes contributes to cerebrovascular complications in bacterial meningitis. METHODS: We performed a nationwide prospective genetic association study in adult community-acquired bacterial meningitis patients. The exons and flanking regions of 16 candidate genes involved in coagulation and fibrinolysis pathways were sequenced. We analyzed whether genetic variation in these genes resulted in a higher risk of cerebrovascular complications, unfavorable outcome and differences in thrombocyte count on admission. RESULTS: From 2006 to 2011, a total of 1101 bacterial meningitis patients were identified of whom 622 supplied DNA for genotyping and passed genetic quality control steps. In 139 patients (22%) the episode of bacterial meningitis was complicated by cerebral infarction, and 188 (30%) had an unfavorable outcome. We identified the functional variant rs494860 in the protein Z (PROZ) gene as our strongest association with occurrence of cerebral infarction (odds ratio (OR) 0.49 (95% confidence interval 0.33-0.73), p = 5.2 × 10-4). After Bonferroni correction for multiple testing no genetic variant was significantly associated (p-value threshold 2.7 × 10-4). CONCLUSION: Our study suggests a functional genetic variation in the PROZ gene, rs494860, may be of importance in bacterial meningitis pathogenesis and cerebral infarction risk. Replication of this finding in other cohort studies populations is needed.

Hyponatraemia in adults with community-acquired bacterial meningitis.

BACKGROUND: Hyponatraemia in adults with bacterial meningitis has been described as a common complication, but its true prevalence and clinical importance are unknown. AIM: To investigate the prevalence, clinical characteristics and consequences of hyponatraemia in bacterial meningitis in adults. DESIGN: Nationwide observational cohort study. METHODS: We prospectively assessed the prevalence and clinical characteristics of hyponatraemia among 696 adults with community-acquired bacterial meningitis. Symptoms and signs on admission, blood and CSF test results, radiological examinations and complications during admission were recorded. RESULTS: Sodium levels were determined at admission in 685/696 episodes of bacterial meningitis (98%). Hyponatraemia (<135 mmol/l) was seen in 208/685 (30%) and was classified as severe (<130 mmol/l) in 38 (6%). Hyponatraemia developed during admission in an additional 53 episodes. Hyponatraemia was not associated with an increase in symptoms, with complications or with unfavourable outcome. Treatment for hyponatraemia was initiated in 16% of episodes, but did not influence its duration. DISCUSSION: Hyponatraemia appears both common and benign in adults with bacterial meningitis. In cases of severe hyponatraemia, we suggest the use of fluid maintenance therapy.