Resistance to neuraminidase inhibitors conferred by an R292K mutation in a human influenza virus H7N9 isolate can be masked by a mixed R/K viral population.

UNLABELLED: We characterized the A/Shanghai/1/2013 virus isolated from the first confirmed human case of A/H7N9 disease in China. The A/Shanghai/1/2013 isolate contained a mixed population of R (65%; 15/23 clones) and K (35%; 8/23 clones) at neuraminidase (NA) residue 292, as determined by clonal sequencing. A/Shanghai/1/2013 with mixed R/K at residue 292 exhibited a phenotype that is sensitive to zanamivir and oseltamivir carboxylate by the enzyme-based NA inhibition assay. The plaque-purified A/Shanghai/1/2013 with dominant K292 (94%; 15/16 clones) showed sensitivity to zanamivir that had decreased by >30-fold and to oseltamivir carboxylate that had decreased by >100-fold compared to its plaque-purified wild-type counterpart possessing dominant R292 (93%, 14/15 clones). In Madin-Darby canine kidney (MDCK) cells, the plaque-purified A/Shanghai/1/2013-NAK292 virus exhibited no reduction in viral titer under conditions of increasing concentrations of oseltamivir carboxylate (range, 0 to 1,000 µM) whereas the replication of the plaque-purified A/Shanghai/1/2013-NAR292 and the A/Shanghai/2/2013 viruses was completely inhibited at 250 µM and 31.25 µM of oseltamivir carboxylate, respectively. Although the plaque-purified A/Shanghai/1/2013-NAK292 virus exhibited lower NA enzyme activity and a higher Km for 2'-(4-methylumbelliferryl)-α-d-N-acetylneuraminic acid than the wild-type A/Shanghai/1/2013-NAR292 virus, the A/Shanghai/1/2013-NAK292 virus formed large plaques and replicated efficiently in vitro. Our results confirmed that the NA R292K mutation confers resistance to oseltamivir, peramivir, and zanamivir in the novel human H7N9 viruses. Importantly, detection of the resistance phenotype may be masked in the clinical samples containing a mixed population of R/K at NA residue 292 in the enzyme-based NA inhibition assay. IMPORTANCE: The neuraminidase (NA) inhibitors oseltamivir and zanamivir are currently the front-line therapeutic options against the novel H7N9 influenza viruses, which possess an S31N mutation that confers resistance to the M2 ion channel blockers. It is therefore important to evaluate the sensitivity of the clinical isolates to NA inhibitors and to monitor for the emergence of resistant variants. We characterized the A/Shanghai/1/2013 (H7N9) isolate which contained a mixed population of R/K at NA residue 292. While the clinical isolate exhibited a phenotype of sensitivity to NA inhibitors using the enzyme-based NA inhibition assay, the plaque-purified A/Shanghai/1/2013 virus with dominant K292 was resistant to zanamivir, peramivir, and oseltamivir. Resistance to NA inhibitors conferred by the R292K mutation in a human influenza virus H7N9 isolate can be masked by a mixed R/K viral population, and this should be taken into consideration while monitoring antiviral resistance in patients with H7N9 infection.

Sudden severe chest pain: thoracic dural arteriovenous fistula aneurysm rupture with intracranial subarachnoid haemorrhage.

Spinal perimedullary arteriovenous fistula (AVF) or dural arteriovenous fistula (DAVF) presenting as intracranial subarachnoid haemorrhage (SAH) is uncommon. A total of 16 cases have been reported to date. A majority of the reports described cervical spinal DAVF, while two other case reports described intracranial SAH secondary to lumbar and thoracic DAVF, respectively. We report a 61-year-old Chinese man with intracranial SAH secondary to thoracic DAVF aneurysm, who presented with sudden, severe chest pain, initially suggestive of aortic dissection/acute myocardial infarction. However, a careful examination of the history and physical signs, followed by appropriate and timely investigations enabled effective treatment to be administered promptly with a good outcome. This serves to illustrate the importance of investigating the entire cerebrospinal system when neurological symptoms and clinical signs suggest extracranial primary pathology.

Infant hearing screening: effects of timeline.

OBJECTIVES: Universal infant hearing screening using otoacoustic emission and auditory brain-stem response audiometry is widely administered to attain the goals of early identification of, and intervention for hearing impairment. Concerns regarding screening specificity have, however, been raised. False positives may result from vernix occlusion in the ear canal or transient middle ear effusion, and can result in substantial costs to health care systems. The current study investigates the effects of age and time interval between tests on hearing assessment results. SETTING & PARTICIPANTS: Three hundred and seventeen positive screens from a 2-stage distortion product otoacoustic emission (DPOAE) screening programme in Hong Kong, who subsequently received diagnostic auditory brainstem response (ABR) assessment and monitoring, were investigated. MAIN OUTCOME MEASURES: Differences in diagnostic ABR results were compared among infants of different ages at tests, and with different time lapses after DPOAE screening. The proportion of those having persistent hearing impairment, conductive loss and impairment of moderate degree or above, were also compared. RESULTS: A significantly higher rate of normal ABR thresholds (60%versus 24%) was noted in infants assessed after age 50 days, and in infants diagnostically assessed with a time lapse of over 20 days post-DPOAE screening (65%versus 42%). CONCLUSIONS: Delaying diagnostic ABR assessment may reveal a higher percentage of normal thresholds, and hence probably higher specificity. Time delay may allow for spontaneous resolution of transient outer and middle ear conditions. However, the goals of early identification and intervention, as well as possible parental anxiety with delayed assessment, should also be considered when reviewing infant hearing screening schedules.

Outcome of moderate and severe traumatic brain injury amongst the elderly in Singapore.

INTRODUCTION: In line with other established protocols, our unit has instituted a standardised protocol for the management of moderate and severe traumatic brain injury since 1996 in our neurointensive care unit. MATERIALS AND METHODS: We reviewed the outcomes, at 6 months' post-injury, in an elderly group aged > or = 64 years (73.86 +/- 8.0 years) and compared them to a younger group aged 20 to 40 years (29.2 +/- 5.7 years) in a cohort of 324 patients. Outcome was dichotomised as favourable (mild and moderate disability but independent; Glasgow Outcome Score [GOS] 4 and 5), unfavourable (severe disability and persistent vegetative state; GOS 2 and 3) and death (GOS 1). RESULTS: In the elderly group, the mortality (55.4%) was slightly more than double that of the younger group (20.9%); 21.5% had an unfavourable outcome (14.2% in the younger group) and only 23% had a favourable outcome (compared to 64.9% in the younger group). The final outcomes were significantly worse in all levels in the elderly group. This was in spite of data showing that the mechanism of injury was of a higher impact in the younger group, with a higher incidence of polytrauma and cervical spine injury. On admission, the mean Glasgow Coma Score (GCS) was 8.3 +/- 3.91 for the elderly group and 8.59 +/- 4.05 for the younger group (P = 0.763). Computed tomography scan showed that the elderly had a higher incidence of mass lesions (extradural haematoma and subdural haematoma) and traumatic subarachnoid haemorrhage. A subgroup (29.2%) of elderly patients had no surgical intervention based on poor clinical/neurological status, premorbid functional status and pre-existing medical conditions, with their family's consent. The GCS of < or = 8, on admission, was significant (P <0.001) in predicting mortality in the elderly. In the elderly group, the female gender had a higher mortality rate (70.4%) than the males (44.7%) (P = 0.19). CONCLUSION: Age must be considered an independent factor in outcome prediction in the elderly with moderate and severe traumatic brain injury. A more conservative approach in the management of an elderly patient with severe head injury may be reasonable given its dismal outcomes after careful dialogue with the relatives.