Antibiotic management of acute pharyngitis in primary care.

The Centre for Health Protection of the Department of Health has convened the Advisory Group on Antibiotic Stewardship Programme in Primary Care (the Advisory Group) to formulate guidance notes and strategies for optimising judicious use of antibiotics and enhancing the Antibiotic Stewardship Programme in Primary Care. Acute pharyngitis is one of the most common conditions among out-patients in primary care in Hong Kong. Practical recommendations on the diagnosis and antibiotic treatment of acute streptococcal pharyngitis are made by the Advisory Group based on the best available clinical evidence, local prevalence of pathogens and associated antibiotic susceptibility profiles, and common local practice.

A comparison of the marginal gaps of lithium disilicate crowns fabricated by two different intraoral scanners.

BACKGROUND: The purpose of this study was to assess marginal gaps of CAD/CAM lithium disilicate crowns constructed using two different intraoral scanners of different generations. METHODS: Twenty four Columbia model lower left molars were prepared for lithium disilicate crowns in a simulated environment by undergraduate students. The crown preparations were scanned by E4D and Trios 3 intraoral scanners and CAD/CAM lithium disilicate crowns designed and manufactured. The crowns were seated onto the original crown preparations and three vertical marginal gap measurements taken at four locations (mid-buccal, mid-lingual, mid-mesial and mid-distal) using a stereomicroscope. The mean marginal gap (MMG) was calculated for each crown and each individual tooth surface. RESULTS: The MMG was not statistically significantly different for the Trios 3 and E4D scanners (P = 0.111). There was no statistically significant effect of measurement location on the tooth on the marginal gap (P = 0.1134). CONCLUSIONS: There was no difference in the MMGs of CAD/CAM lithium disilicate crowns constructed using two different intraoral scanners of different generations. Within the limitations of this study, the advances in scanning technology have produced small and insignificant improvements in the accuracy of crown margins.

Seasonal shifts in the presence of pathogenic leptospires, Escherichia coli, and physicochemical properties in coastal rivers and streams of Puerto Rico.

Leptospirosis is an emerging zoonotic disease in the Caribbean region and the island of Puerto Rico. Information on the presence of pathogenic Leptospira in rivers and streams of Puerto Rico is currently lacking. This study aimed to evaluate seasonal shifts in the presence of pathogenic leptospires and the level of Escherichia coli from 32 coastal locations in Puerto Rico's dry and wet seasons. Physicochemical parameters (temperature, salinity, pH, and dissolved oxygen) were determined at each site. The temperature (25.8 °C) and pH (average 7.6) values were all within acceptable USEPA regulatory standards. Thirty-eight percent of the sites of the dry season and 28% of the wet season sites contained dissolved oxygen levels ≤4 mg L-1 , which is relatively low. In the dry season, 19 sites (59%) and 18 (56%) of the wet season sites had E. coli counts >410 most probable number (MPN) 100 ml-1 and would be considered unsafe for recreational use. The lipl32 gene quantitative polymerase chain reaction assay was used for the detection of pathogenic leptospires in the samples. Low concentrations of pathogenic leptospires (<60 genome copies 100 ml-1 ) at Camuy, Espíritu Santo, Río Guayanilla, Quebrada Majagual, and Río Fajardo were detected during the wet season. Pathogenic leptospires were detected (∼40 genome copies 100 ml-1 ) at only one site, Loíza, during the dry season. There was no predictable relationship between the physicochemical parameters, concentrations of E. coli, and the presence of pathogenic leptospires in water samples.

Auditory system plasticity in children after long periods of complete deafness.

Deaf children fitted with a cochlear implant provide a unique opportunity to examine the effects of auditory deprivation on the maturation of the human auditory system. We compared cortical evoked potentials recorded in implanted and normal-hearing children and found that age-dependent latency changes for the P1 component, fitted to a decaying exponential curve, showed the same rate of maturation. For implanted children, however, maturational delays for P1 latency approximated the period of auditory deprivation prior to implantation. This indicates the auditory system does not mature without stimulation. Nonetheless, the auditory system retains its plasticity during the period of deafness since the re-introduction of stimulation by the cochlear implant resumes the normal maturational sequence.

Spatial mislocalization of EEG electrodes -- effects on accuracy of dipole estimation.

OBJECTIVE: The estimation of cortical current activity from scalp-recorded potentials is a complicated mathematical problem that requires fairly precise knowledge of the location of the scalp electrodes. It is expected that spatial mislocalization of electrodes will introduce errors in this estimation. The present study uses simulated and real data to quantify these errors for dipole current sources in a spherical head model. METHODS: A 3-dimensional digitizer was used to locate the positions of 31 scalp electrodes placed on the head according to the 10-20 system in 10 normal subjects. Dipole localizations were performed on auditory evoked potentials (AEPs) collected from these subjects. RESULTS: Computer simulations with several dipole source configurations suggest that errors in locations and orientations on the order of 5 mm and 5 degrees, respectively, are possible for electrode mislocalizations of about 5 degrees. In actual experimental settings, digitized electrode positions were typically mislocalized by an average of about 4 degrees from their standard 10-20 positions on a spherical model. These differences in electrode positions translated to mean differences of about 8 mm in dipole locations and 5 degrees in dipole orientations. CONCLUSIONS: Dipole estimation errors due to electrode mislocalizations are within the limits of errors due to other modeling approximations and noise.

Maturation of human central auditory system activity: evidence from multi-channel evoked potentials.

OBJECTIVE: The purpose of this study was to evaluate central auditory system maturation based on detailed data from multi-electrode recordings of long-latency auditory evoked potentials (AEPs). METHODS: AEPs were measured at 30 scalp-electrode locations from 118 subjects between 5 and 20 years of age. Analyses focused on age-related latency and amplitude changes in the P1, N1b, P2, and N2 peaks of the AEPs generated by a brief train of clicks presented to the left ear. RESULTS: Substantial and unexpected changes that extend well into adolescence were found for both the amplitude and latency of the AEP components. While the maturational changes in latency followed a pattern of gradual change, amplitude changes tended to be more abrupt and step-like. Age-related latency decreases were largest for the P1 and N1b peaks. In contrast, P2 latency did not change significantly and the N2 peak increased in latency as a function of age. Abrupt changes in P1, P1-N1b, and N2 peak amplitude (also RMS amplitude) were observed around age 10 at the lateral electrode locations C3 and C4, but not at the midline electrodes Cz and Fz. These changes in amplitude coincided with a sharp increase and plateau in AEP peak and RMS amplitude variability from 9 to 11 years of age. CONCLUSIONS: These analyses demonstrated that the observed pattern of AEP maturation depends on the scalp location at which the responses are recorded. The distinct maturational time courses observed for individual AEP peaks support a model of AEP generation in which activity originates from two or more at least partly independent central nervous system pathways. A striking parallel was observed between previously reported maturational changes in auditory cortex synaptic density and, in particular, the age-related changes in P1 amplitude. The results indicate that some areas of the brain activated by sound stimulation have a maturational time course that extends into adolescence. Maturation of certain auditory processing skills such as speech recognition in noise also has a prolonged time course. This raises the possibility that the emergence of adult-like auditory processing skills may be governed by the same maturing neural processes that affect AEP latency and amplitude.

Plasticity in the adult human central auditory system: evidence from late-onset profound unilateral deafness.

Experience-related changes in central nervous system (CNS) activity have been observed in the adult brain of many mammalian species, including humans. In humans, late-onset profound unilateral deafness creates an opportunity to study plasticity in the adult CNS consequent to monaural auditory deprivation. CNS activity was assessed by measuring long-latency auditory evoked potentials (AEPs) recorded from teens and adults with late-onset (post-childhood) profound unilateral deafness. Compared to monaurally stimulated normal-hearing subjects, the AEPs recorded from central electrode sites located over auditory cortical areas showed significant increases in inter-hemispheric waveform cross-correlation coefficients, and in inter-hemispheric AEP peak amplitude correlations. These increases provide evidence of substantial changes from the normal pattern of asymmetrical (contralateral > ipsilateral amplitude) and asynchronous (contralateral earlier than ipsilateral) central auditory system activation in the normal-hearing population to a much more symmetrical and synchronous activation in the unilaterally deaf. These cross-sectional analyses of AEP data recorded from the unilaterally deaf also suggest that the changes in cortical activity occur gradually and continue for at least 2 years after the onset of hearing loss. Analyses of peak amplitude correlations suggest that the increased inter-hemispheric symmetry may be a consequence of changes in the generators producing the N (approximately 100 ms peak latency) potential. These experience-related changes in central auditory system activity following late-onset profound unilateral deafness thus provide evidence of the presence and the time course of auditory system plasticity in the adult brain.

Maturational delays in cortical evoked potentials in cochlear implant users.

We studied the effects of prolonged auditory deprivation in children in whom auditory stimulation was restored by a cochlear implant. The latency of the P1 component of the late cortical potential was used as the indicator of auditory system maturation. For normal-hearing children there is a gradual evolution of evoked potential features that extends through adolescence with P1 latency becoming adult-like at about age 15. It appears that maturation of P1 latency in normal and implanted children occurs at the same rate, but the time to maturity in implanted subjects is delayed by an amount approximately equal to the duration of deafness.

Integrated mismatch negativity (MMNi): a noise-free representation of evoked responses allowing single-point distribution-free statistical tests.

If the repeated presentation of a single (standard) auditory stimulus is randomly interspersed with a second acoustically different (deviant) stimulus, the cortical activity evoked by the deviant stimulus can contain a negative component known as the mismatch negativity (MMN). The MMN is derived by subtracting the averaged response evoked by the standard stimulus from that evoked by the deviant stimulus. When the magnitude of the response is small or the signal-to-noise ratio is poor, it is difficult to judge the presence or absence of the MMN simply by visual inspection, and statistical detection techniques become necessary. A method of analysis is proposed to quantify the magnitude and statistically evaluate the presence of the MMN based on time-integrated evoked responses. This paper demonstrates the use of this integrated mismatch negativity (MMNi) analysis to detect the MMN evoked by stimulus contrasts near the perceptual threshold of two subjects. The MMNi, by virtue of being equivalent to a low-pass filtered response, presents an almost noise-free estimate of MMN magnitude. A single measure of the integrated evoked response at a fixed time point is used in a distribution-free statistic that compares the magnitude of the averaged response evoked by the deviant stimulus with a magnitude distribution derived from 200 subaveraged responses to the standard stimulus (with the number of sweeps per average equal to that of the deviant stimulus). This allows a calculation of the exact probability for the null hypothesis that the negative magnitude of the response evoked by the deviant stimulus is drawn from the magnitude distribution of responses evoked by the standard stimulus. Rejection of this hypothesis provides objective evidence of the presence of the MMN.

Psychological epidemic in Hong Kong. I. Epidemiological study.

A total of 413 school students were taken ill with symptoms from an alleged poisonous gas affecting two different geographic locations at the same time and without influencing the residents in the neighbourhood. Symptoms were mainly subjective and almost all were discharged from hospital the same day. Vigorous endeavours by authorities had failed to discover the offending agent. By the use of epidemiological methods, the present study attempted to investigate the nature of and the significant contributing factors related to the episode. The psychological nature was confirmed both by demonstration of positive characteristics as well as by the exclusion of organicity. There was no direct evidence that teachers, headmasters, parents or the mass media had significant influence on the aetiology of the epidemic, albeit their influence could still be an indirect one. Regarding symptom formation, there was evidence that peer influences were more important than an individual's own previous experiences.

Psychological epidemic in Hong Kong. II. Psychological and physiological characteristics of children who were affected.

A double blind retrospective study was carried out on a sample of children who were affected in a mysterious gas poisoning epidemic together with controls drawn from the same school. The dependent measures employed were the Junior Eysenck Personality Questionnaire (JEPQ), a Hypnotic Susceptibility Scale (HSC), Heart Rate (HR) and Skin Potential Response (SPR). A vigilance task was administered during assessment of the latter two variables. The affected children had significantly higher HR together with a marginal increase in SPR. It is proposed that constitutional factors play an important role in determining whether an individual is affected in such an epidemic.

The effects of sensory hearing loss on cochlear filter times estimated from auditory brainstem response latencies.

Derived-band auditory brainstem responses (ABRs) were obtained in 43 normal-hearing and 80 cochlear hearing-impaired individuals using clicks and high-pass noise masking. The response times across the cochlea [the latency difference between wave V's of the 5.7- and 1.4-kHz center frequency (CF) derived bands] were calculated for five levels of click stimulation ranging from 53 to 93 dB p.-p.e. SPL (23 to 63 dB nHL) in 10-dB steps. Cochlear response times appeared to shorten significantly with hearing loss, especially when the average pure tone (1 to 8 kHz) hearing loss exceeded 30 dB. Examination of derived-band latencies indicates that this shortening is due to a dramatic decrease of wave V latency in the lower CF derived band. Estimates of cochlear filter times in terms of the number of periods to maximum response (Nmax) were calculated from derived-band latencies corrected for gender-dependent cochlear transport and neural conduction times. Nmax decreased as a function of hearing loss, especially for the low CF derived bands. The functions were similar for both males and females. These results are consistent with broader cochlear tuning due to peripheral hearing loss. Estimating filter response times from ABR latencies enhances objective noninvasive diagnosis and allows delineation of the differential effects of pathology on the underlying cochlear mechanisms involved in cochlear transport and filter build-up times.

Maturation of the mismatch negativity: effects of profound deafness and cochlear implant use.

The use of cochlear implants to restore auditory sensation in deaf children is increasing, with a trend toward earlier implantation. However, little is known about how auditory deprivation and subsequent cochlear implant use affect the maturing human central auditory system. Our previous studies have demonstrated that the obligatory auditory evoked potentials (AEPs) of implanted children are very different from those of normal-hearing children. Unlike the obligatory potentials, which primarily reflect neural responses to stimulus onset, the mismatch negativity (MMN) provides a neurophysiological measure of auditory short-term memory and discrimination processes. The purpose of this investigation is to review our studies of the effects of auditory deprivation due to profound deafness and cochlear implant use on the maturation of the MMN in children, placed in the context of overall age-related changes in the AEPs. The development and application of a statistical technique to assess the MMN in individuals is also reviewed. Results show that although the morphology of the obligatory AEPs is substantially altered by the absence of a normal N(1) peak, the MMN is robustly present in a group of implanted children who have good spoken language perception through their device. Differences exist in the scalp distribution of the MMN between implanted and normal-hearing children. Specifically, the MMN appears to be more symmetrical in amplitude over both hemispheres, whereas it is initially much larger over the contralateral hemisphere in normal-hearing children. These findings suggest that, compared to N(1), the MMN is a better measure of basic auditory processes necessary for the development of spoken language perception skills in profoundly deaf children and adults who use a cochlear implant.