Increasing rhinovirus prevalence in paediatric intensive care patients since the SARS-CoV2 pandemic.

BACKGROUND: Rhinovirus (HRV) is a significant seasonal pathogen in children. The emergence of SARS-CoV2, and the social restrictions introduced in, disrupted viral epidemiology. Here we describe the experience of Great Ormond Street Hospital (GOSH), where HRV almost entirely disappeared from the paediatric intensive care units (PICU) during the first national lockdown and then rapidly re-emerged with a fast-increasing incidence, leading to concerns about possible nosocomial transmission in a vulnerable population. OBJECTIVES: To describe alterations in HRV infection amongst PICU patients at GOSH since the emergence of SARS-COV2 STUDY DESIGN: 10,950 nasopharyngeal aspirate viral PCR samples from GOSH PICU patients from 2019 to 2023 were included. 3083 returned a positive result for a respiratory virus, with 1530 samples positive for HRV. 66 HRV isolates from August 2020 - Jan 2021, the period of rapidly increasing HRV incidence, were sequenced. Electronic health record data was retrospectively collected for the same period. RESULTS: Following a reduction in the incidence of HRV infection during the first national lockdown, multiple genotypes of HRV emerged amongst GOSH PICU patients, with the incidence of HRV infection rapidly surging to levels higher than that seen prior to the emergence of SARS-CoV2 and continuing to circulate at increased incidence year-round. CONCLUSIONS: The incidence of HRV infection amongst GOSH PICU patients is markedly higher than prior to the emergence of SARS-CoV2, a pattern not seen in other respiratory viruses. The increased burden of HRV-infection in vulnerable PICU patients has both clinical and infection prevention and control Implications.

Pericyte derived chemokines amplify neutrophil recruitment across the cerebrovascular endothelial barrier.

Excessive neutrophil extravasation can drive immunopathology, exemplified in pyogenic meningitis caused by Streptococcus pneumoniae infection. Insufficient knowledge of the mechanisms that amplify neutrophil extravasation has limited innovation in therapeutic targeting of neutrophil mediated pathology. Attention has focussed on neutrophil interactions with endothelia, but data from mouse models also point to a role for the underlying pericyte layer, as well as perivascular macrophages, the only other cell type found within the perivascular space in the cerebral microvasculature. We tested the hypothesis that human brain vascular pericytes (HBVP) contribute to neutrophil extravasation in a transwell model of the cerebral post-capillary venule. We show that pericytes augment endothelial barrier formation. In response to inflammatory cues, they significantly enhance neutrophil transmigration across the endothelial barrier, without increasing the permeability to small molecules. In our model, neither pericytes nor endothelia responded directly to bacterial stimulation. Instead, we show that paracrine signalling by multiple cytokines from monocyte derived macrophages drives transcriptional upregulation of multiple neutrophil chemokines by pericytes. Pericyte mediated amplification of neutrophil transmigration was independent of transcriptional responses by endothelia, but could be mediated by direct chemokine translocation across the endothelial barrier. Our data support a model in which microbial sensing by perivascular macrophages generates an inflammatory cascade where pericytes serve to amplify production of neutrophil chemokines that are translocated across the endothelial barrier to act directly on circulating neutrophils. In view of the striking redundancy in inflammatory cytokines that stimulate pericytes and in the neutrophil chemokines they produce, we propose that the mechanism of chemokine translocation may offer the most effective therapeutic target to reduce neutrophil mediated pathology in pyogenic meningitis.

Streptococcus pneumoniae interactions with the complement system.

Host innate and adaptive immunity to infection with Streptococcus pneumoniae is critically dependent on the complement system, demonstrated by the high incidence of invasive S. pneumoniae infection in people with inherited deficiency of complement components. The complement system is activated by S. pneumoniae through multiple mechanisms. The classical complement pathway is activated by recognition of S. pneumoniae by C-reactive protein, serum amyloid P, C1q, SIGN-R1, or natural or acquired antibody. Some S. pneumoniae strains are also recognised by ficolins to activate the mannose binding lectin (MBL) activation pathway. Complement activation is then amplified by the alternative complement pathway, which can also be activated by S. pneumoniae directly. Complement activation results in covalent linkage of the opsonic complement factors C3b and iC3b to the S. pneumoniae surface which promote phagocytic clearance, along with complement-mediated immune adherence to erythrocytes, thereby protecting against septicaemia. The role of complement for mucosal immunity to S. pneumoniae is less clear. Given the major role of complement in controlling infection with S. pneumoniae, it is perhaps unsurprising that S. pneumoniae has evolved multiple mechanisms of complement evasion, including the capsule, multiple surface proteins, and the toxin pneumolysin. There is considerable variation between S. pneumoniae capsular serotypes and genotypes with regards to sensitivity to complement which correlates with ability to cause invasive infections. However, at present we only have a limited understanding of the main mechanisms causing variations in complement sensitivity between S. pneumoniae strains and to non-pathogenic streptococci.

Streptococcus pneumoniae meningitis and the CNS barriers.

Streptococcus pneumoniae (SPN) is a globally significant cause of meningitis, the pathophysiology of which involves damage to the brain by both bacterial virulence factors and the host inflammatory response. In most cases of SPN meningitis bacteria translocate from the blood into the central nervous system (CNS). The principal site of SPN translocation into the CNS is not known, with possible portals of entry proposed to be the cerebral or meningeal blood vessels or the choroid plexus. All require SPN to bind to and translocate across the vascular endothelial barrier, and subsequently the basement membrane and perivascular structures, including an additional epithelial barrier in the case of the blood-CSF barrier. The presence of SPN in the CNS is highly inflammatory resulting in marked neutrophilic infiltration. The secretion of toxic inflammatory mediators by activated neutrophils within the CNS damages pathogen and host alike, including the non-replicative neurons which drives morbidity and mortality. As with the translocation of SPN, the recruitment of neutrophils into the CNS in SPN meningitis necessitates the translocation of neutrophils from the circulation across the vascular barrier, a process that is tightly regulated under basal conditions - a feature of the 'immune specialization' of the CNS. The brain barriers are therefore central to SPN meningitis, both through a failure to exclude bacteria and maintain CNS sterility, and subsequently through the active recruitment and/or failure to exclude circulating leukocytes. The interactions of SPN with these barriers, barrier inflammatory responses, along with their therapeutic implications, are explored in this review.

Use of ß-D-glucan in diagnosis of suspected Pneumocystis jirovecii pneumonia in adults with HIV infection.

OBJECTIVES: An elevated serum (1-3)-ß-D-glucan (BDG) concentration has high sensitivity for a diagnosis of Pneumocystis pneumonia (PCP) in people with HIV (PWH). At the current manufacturer-recommended positive threshold of 80 pg/mL (Fungitell), specificity for PCP is variable and other diagnostic tests are required. We evaluated the utility of serum BDG for diagnosis of suspected PCP in PWH at three inner-London hospitals to determine BDG concentrations for diagnosis and exclusion of PCP. METHODS: From clinical case records, we abstracted demographic and clinical information and categorised patients as having confirmed or probable PCP, or an alternative diagnosis. We calculated sensitivity, specificity and positive predictive value (PPV) of serum BDG concentrations >400 pg/mL and negative predictive value (NPV) of BDG <80 pg/mL. RESULTS: 76 patients were included; 29 had laboratory-confirmed PCP, 17 had probable PCP and 30 had an alternative diagnosis. Serum BDG >400 pg/mL had a sensitivity of 83%, specificity of 97% and PPV 97% for diagnosis of PCP; BDG <80 pg/mL had 100% NPV for exclusion of PCP. CONCLUSIONS: In PWH with suspected PCP, BDG <80 pg/mL excludes a diagnosis of PCP, whereas BDG concentrations >400 pg/mL effectively confirm the diagnosis. Values 80-400 pg/mL should prompt additional diagnostic tests.

Acute bacterial meningitis.

PURPOSE OF REVIEW: Community-acquired bacterial meningitis is a continually changing disease. This review summarises both dynamic epidemiology and emerging data on pathogenesis. Updated clinical guidelines are discussed, new agents undergoing clinical trials intended to reduce secondary brain damage are presented. RECENT FINDINGS: Conjugate vaccines are effective against serotype/serogroup-specific meningitis but vaccine escape variants are rising in prevalence. Meningitis occurs when bacteria evade mucosal and circulating immune responses and invade the brain: directly, or across the blood-brain barrier. Tissue damage is caused when host genetic susceptibility is exploited by bacterial virulence. The classical clinical triad of fever, neck stiffness and headache has poor diagnostic sensitivity, all guidelines reflect the necessity for a low index of suspicion and early Lumbar puncture. Unnecessary cranial imaging causes diagnostic delays. cerebrospinal fluid (CSF) culture and PCR are diagnostic, direct next-generation sequencing of CSF may revolutionise diagnostics. Administration of early antibiotics is essential to improve survival. Dexamethasone partially mitigates central nervous system inflammation in high-income settings. New agents in clinical trials include C5 inhibitors and daptomycin, data are expected in 2025. SUMMARY: Clinicians must remain vigilant for bacterial meningitis. Constantly changing epidemiology and emerging pathogenesis data are increasing the understanding of meningitis. Prospects for better treatments are forthcoming.

Bedaquiline as Treatment for Disseminated Nontuberculous Mycobacteria Infection in 2 Patients Co-Infected with HIV.

Nontuberculous mycobacteria can cause disseminated infections in immunocompromised patients and are challenging to treat because of antimicrobial resistance and adverse effects of prolonged multidrug treatment. We report successful treatment with bedaquiline, a novel antimycobacterial drug, as part of combination therapy for 2 patients with disseminated nontuberculous mycobacteria co-infected with HIV.

Correction to: Blood transcriptomic discrimination of bacterial and viral infections in the emergency department: a multi-cohort observational validation study.

An amendment to this paper has been published and can be accessed via the original article.

Blood transcriptomic discrimination of bacterial and viral infections in the emergency department: a multi-cohort observational validation study.

BACKGROUND: There is an urgent need to develop biomarkers that stratify risk of bacterial infection in order to support antimicrobial stewardship in emergency hospital admissions. METHODS: We used computational machine learning to derive a rule-out blood transcriptomic signature of bacterial infection (SeptiCyte™ TRIAGE) from eight published case-control studies. We then validated this signature by itself in independent case-control data from more than 1500 samples in total, and in combination with our previously published signature for viral infections (SeptiCyte™ VIRUS) using pooled data from a further 1088 samples. Finally, we tested the performance of these signatures in a prospective observational cohort of emergency department (ED) patients with fever, and we used the combined SeptiCyte™ signature in a mixture modelling approach to estimate the prevalence of bacterial and viral infections in febrile ED patients without microbiological diagnoses. RESULTS: The combination of SeptiCyte™ TRIAGE with our published signature for viral infections (SeptiCyte™ VIRUS) discriminated bacterial and viral infections in febrile ED patients, with a receiver operating characteristic area under the curve of 0.95 (95% confidence interval 0.90-1), compared to 0.79 (0.68-0.91) for WCC and 0.73 (0.61-0.86) for CRP. At pre-test probabilities 0.35 and 0.72, the combined SeptiCyte™ score achieved a negative predictive value for bacterial infection of 0.97 (0.90-0.99) and 0.86 (0.64-0.96), compared to 0.90 (0.80-0.94) and 0.66 (0.48-0.79) for WCC and 0.88 (0.69-0.95) and 0.60 (0.31-0.72) for CRP. In a mixture modelling approach, the combined SeptiCyte™ score estimated that 24% of febrile ED cases receiving antibacterials without a microbiological diagnosis were due to viral infections. Our analysis also suggested that a proportion of patients with bacterial infection recovered without antibacterials. CONCLUSIONS: Blood transcriptional biomarkers offer exciting opportunities to support precision antibacterial prescribing in ED and improve diagnostic classification of patients without microbiologically confirmed infections.

Analysis tools to quantify dissemination of pathology in zebrafish larvae.

We describe new open source software called QuantiFish for rapid quantitation of fluorescent foci in zebrafish larvae, to support infection research in this animal model. QuantiFish extends the conventional measurements of bacterial load and number of bacterial foci to include measures for dissemination of infection. These are represented by the proportions of bacteria between foci and their spatial distribution. We showcase these measures by comparison of intravenous and hindbrain routes of Mycobacterium marinum infection, which are indistinguishable by measurement of bacterial load and not consistently differentiated by the number of bacterial foci. The intravenous route showed dose dependent dissemination of infection, reflected by increased spatial dispersion of bacteria and lower proportions of bacteria distributed across many foci. In contrast, hindbrain infection resulted in localised disease, limited to a smaller area and higher proportions of bacteria distributed across fewer foci. The application of QuantiFish may extend beyond models of infection, to study other pathologies such as metastatic cancer.

Blood transcriptomic diagnosis of pulmonary and extrapulmonary tuberculosis.

BACKGROUND. Novel rapid diagnostics for active tuberculosis (TB) are required to overcome the time delays and inadequate sensitivity of current microbiological tests that are critically dependent on sampling the site of disease. Multiparametric blood transcriptomic signatures of TB have been described as potential diagnostic tests. We sought to identify the best transcript candidates as host biomarkers for active TB, extend the evaluation of their specificity by comparison with other infectious diseases, and to test their performance in both pulmonary and extrapulmonary TB. METHODS. Support vector machine learning, combined with feature selection, was applied to new and previously published blood transcriptional profiles in order to identify the minimal TB­specific transcriptional signature shared by multiple patient cohorts including pulmonary and extrapulmonary TB, and individuals with and without HIV-1 coinfection. RESULTS. We identified and validated elevated blood basic leucine zipper transcription factor 2 (BATF2) transcript levels as a single sensitive biomarker that discriminated active pulmonary and extrapulmonary TB from healthy individuals, with receiver operating characteristic (ROC) area under the curve (AUC) scores of 0.93 to 0.99 in multiple cohorts of HIV-1-negative individuals, and 0.85 in HIV-1-infected individuals. In addition, we identified and validated a potentially novel 4-gene signature comprising CD177, haptoglobin, immunoglobin J chain, and galectin 10 that discriminated active pulmonary and extrapulmonary TB from other febrile infections, giving ROC AUCs of 0.94 to 1. CONCLUSIONS. Elevated blood BATF2 transcript levels provide a sensitive biomarker that discriminates active TB from healthy individuals, and a potentially novel 4-gene transcriptional signature differentiates between active TB and other infectious diseases in individuals presenting with fever. FUNDING. MRC, Wellcome Trust, Rosetrees Trust, British Lung Foundation, NIHR.

Case report: passive transfer of hepatitis B antibodies from intravenous immunoglobulin.

BACKGROUND: Prior to initiating immunosuppressive therapy in the treatment of autoimmune inflammatory conditions, it is a requirement to screen for certain viral serology, including hepatitis B (HBV). A positive result may indicate the need for antiviral therapy, or contraindicate immunosuppression all together. An accurate interpretation of serological markers is therefore imperative in order to treat patients appropriately. We present a case of passive anti-HBV antibody transfer following intravenous immunoglobulin (IVIg) infusion, in which misinterpretation of serology results almost led to inappropriate treatment with antiviral therapy and the withholding of immunosuppressive agents. This phenomenon has been previously reported, but awareness remains limited. CASE PRESENTATION: A 50 year old Caucasian gentleman with a history of allogeneic haematopoietic stem cell transplant for transformed follicular lymphoma was admitted to hospital with recurrent respiratory tract infections. Investigation found him to be hypogammaglobulinaemic, and he was thus given 1 g/kg of intravenous immunoglobulin. The patient also disclosed a 3-week history of painful, swollen joints, leading to a diagnosis of seronegative inflammatory polyarthritis. Prior to initiating long term immunosuppression, viral screening found hepatitis B serology suggestive of past infection, with positive results for both anti-HBc and anti-HBs antibody, but negative HBV DNA. In response, prednisolone was weaned and the local hepatology team recommended commencement of lamivudine. Having been unable to identify a source of infection, the case was reported to the local blood centre, who tested a remaining vial from the same batch of IVIg and found it to be anti-HBc and anti-HBs positive. Fortunately the blood products were identified and tested prior to the patient initiating HBV treatment, and the effect of a delay in starting disease-modifying therapy was inconsequential in light of an excellent response to first-line therapies. CONCLUSION: Misinterpretation of serology results following IVIg infusion may lead to significant patient harm, including unnecessary antiviral administration, the withholding of treatments, and psychosocial damage. This is especially pertinent at a time when we have an ever increasing number of patients being treated with IVIg for a wide array of immune-mediated disease. Passive antibody transfer should be considered wherever unexpected serological changes are identified.

Systemic vasculitis: a dual diagnosis?

The authors describe a 25-year-old male with systemic vasculitis fulfilling the American College of Rheumatology classification criteria for both granulomatosis with polyangiitis (Wegener's granulomatosis) and polyarteritis nodosa. The patient was diagnosed with granulomatosis with polyangiitis following a mediastinal biopsy which revealed necrotising granulomas of the large airways, a positive cytoplasmic antineutrophil cytoplasmic antibodies and high antiproteinase 3 antibody titre. He then developed acute right-sided abdominal and testicular pain as well as areas of hyperaesthesia and parasthesiae on both lower limbs. He was found to have focal crescentic glomerulonephritis and mononeuritis multiplex, in keeping with his diagnosis of granulomatosis with polyangiitis, as well as two areas of infarction in his right testicle and multiple aneurysms of his hepatic and right renal arteries, more typical of polyarteritis nodosa. His symptoms developed 6 weeks after hepatitis B vaccination, which may have played an aetiological role.