Streptococcus pneumoniae antibiotic resistance in Northern Territory children in day care.

BACKGROUND: There is evidence that the rapid rise in Streptococcus pneumoniae (SP) antimicrobial resistance seen in other countries may have commenced in Australia. Streptococcus pneumoniae carriage and resistance levels are described for urban Northern Territory children in day care. METHODS: A prospective cohort study was conducted of 250 children in nine Darwin day care centres between 24 March and 15 September 1997. Each fortnight nasopharyngeal swabs were collected from children, and parents were interviewed about medications administered. RESULTS: Streptococcus pneumoniae was detected in 52% (1028/1974) of all nasopharyngeal swabs. Streptococcus pneumoniae was isolated from 92% (231/250) of children at some time. Penicillin resistance was found in 30% (312/1028) of isolates using a screening test. Of these, 256 (82%) had resistance confirmed by E-test. Two hundred and one (20% of all isolates) had intermediate penicillin resistance and 55 (5% of all isolates) had high level resistance. Ceftriaxone resistance was found in 19% of children's first isolates. Resistance to other antibiotics was also common: co-trimoxazole 45%, erythromycin 17%, tetracycline 17% and chloramphenicol 13%. A total of 17% (172/1028) of the isolates were multiresistant. The average fortnightly proportion of children given antibiotics was 16% (405/2476). CONCLUSION: Levels of intermediate and high level penicillin resistance in this day care population are consistent with previous data from the Northern Territory, and considerably higher than the rest of Australia. The national trend of increasing pencillin resistance is likely to continue.

Middle ear effusion: rate and risk factors in Australian children attending day care.

There have been no previous longitudinal studies of otitis media conducted in non-Aboriginal Australian children. This paper describes the rate and risk factors for middle ear effusion (MEE) in children attending day care in Darwin, Australia. A prospective cohort study of 252 children under 4 years was conducted in 9 day care centres over 12 fortnights between 24 March and 15 September 1997. Tympanometry was conducted fortnightly and multivariate analysis used to determine risk factors predicting MEE. The outcome of interest was the rate of type B tympanograms per child detected in either ear at fortnightly examinations. After adjusting for clustering by child, MEE was detected on average 4.4 times in 12 fortnights (37% of all examinations conducted). Risk factors associated with presence of effusion were younger age, a family history of ear infection, previous grommets (tympanostomy tubes), ethnicity and the day care centre attended. A history of wheeze appeared protective. These effects were modest (RR 0.57-1.70). Middle ear effusion is very common in children attending day care in Darwin. This has clinical importance, since MEE during early childhood may affect optimal hearing, learning and speech development. There is little scope for modification for many of the risk factors for MEE predicted by this model. Further study of the day care environment is warranted.

Circadian rhythm dependent kanamycin-induced hearing loss in rodents assessed by auditory brainstem responses.

An antimicrobial agent, kanamycin, has been shown to produce as an untoward effect, ototoxicity. The purpose of this study was to investigate differential effects of kanamycin ototoxicity as a function of Rx timing with regard to circadian rhythms. Four groups of comparable weight Sprague-Dawley rats received a daily subcutaneous dosage of 225 mg/kg kanamycin sulfate with each receiving the antibiotic at a different time: 8 AM (8A), 2 PM (2P), 8 PM (8P), and 2 AM (2A). The rats were housed in separate cages, in a room on a light-dark (12:12) illumination cycle with light between 6 AM and 6 PM. Hearing loss was assessed with the auditory brainstem response (ABR) using pure tone stimuli at 8, 16, 24, and 32 kHz. ABR measures were obtained before dosing began and 2, 4, and 6 weeks after the initial dosing. Kanamycin produced a hearing loss which reflected the total dosage given to each group. Significant differences in physiologic thresholds were observed for both timing of the daily dosage (p less than 0.05), and the 2, 4 and 6 week testings (p less than 0.001). After 2 weeks, the 8A group showed an average hearing loss of 11.5 dB at 32 kHz, with the other timed treatment groups exhibiting minimal effects (3.0-6.5 dB). For the 8A group at this frequency, the loss progressed at 4 (19.5 dB) and 6 (22.5 dB) weeks. The 2P group after 4 weeks exhibited similar losses as the 8A group for this frequency, with the loss at 6 weeks being even greater (34.0 dB). The 8P and 2A groups exhibited only slight losses over all frequencies.(ABSTRACT TRUNCATED AT 250 WORDS)

Gentamicin-induced chronotoxicity: use of body temperature as a circadian marker rhythm.

Aminoglycoside antibiotics produce varying degrees of ototoxicity, dependent on dosage time, in animals synchronized for rhythm study. Herein, we illustrate the use of an economical and reliable system to telemeter body temperature of laboratory animals as an endogenous marker rhythm for gentamicin-induced ototoxicity. Two groups of 3 male Sprague-Dawley rats (250-400 gm) were housed in separate cages in a temperature-controlled room programmed with a 12:12 LD schedule and monitored for hearing thresholds at the frequencies of 8kHz, 16 kHz, 24 kHz and 32 kHz at 2-week intervals. Each rat was dosed with 100 mg/kg/day gentamicin subcutaneously for a duration of 28 days. The animals from one group were dosed at their daily temperature maximum, while the animals of the other group were dosed at their daily temperature minimum. Both after 14 and 28 days of gentamicin treatment there was no important changes in auditory thresholds from baseline values when treatment was timed daily to the circadian peak of body temperature. Animals dosed daily at the trough of the circadian temperature rhythm evidenced an auditory threshold shift of between 5 and 25 dB after 14 days of treatment and a total hearing loss (80-90 dB) after 28 days of such treatment. These results document a dramatically greater level of hearing loss induced in those animals dosed with gentamicin at the body temperature trough (diurnal rest span) as compared to those dosed at the acrophase (nocturnal activity span). The findings indicate that the peak and trough of the circadian pattern of body temperature serve as meaningful markers of the resistance and susceptibility, respectively, of gentamicin-induced ototoxicity in rodent models.

Primary modality for speech perception in children with normal and impaired hearing.

The relationships between each of seven predictor variables and the relative degree to which 84 normal and hearing-impaired children used audition or vision in their perception of word stimuli were investigated. The children's relative use of audition or vision was assessed by the auditory-visual presentation of monosyllabic word stimuli in which the visual word stimuli were in conflict with those presented acoustically. Six of the seven predictor variables were significantly correlated with the performance scores obtained within the auditory-visual conflict condition. Only pure-tone average hearing level and auditory word identification performance, however, made unique contributions toward predicting the degree to which audition or vision was used in the perception of the word stimuli. We concluded that the relative use of audition or vision was almost completely related to their auditory capabilities as represented by the children's unaided threshold sensitivity and aided speech reception performance.

Methyl mercury ototoxicity in mice determined by auditory brainstem responses.

Mice of the C57 B1/6 strain were used to assess auditory deficits due to methyl mercury chloride intoxication. Auditory Brainstem Responses were obtained to pure-tone stimuli from 4 to 78 kHz. Physiologic thresholds were compared with behavioral methods for determining audibility in mice. Two dosage levels were studied; 4 and 8 mg/kg. Recordings were taken weekly, for each mouse, for 3 consecutive weeks after initial injection. Analysis of physiologic threshold and latency indicated that methyl mercury chloride causes auditory deficits at all frequencies tested with the greater effect in the higher frequencies. Additionally, latencies indicated nerve conduction hypersensitivity in the brainstem.

The acoustic cricothyroid response in the rat.

Contraction of the cricothyroid muscle (CTM) in the bat is known to raise vocal pitch. An electrode was placed on the CTM of 12 adult lightly-anesthetized rats and electromyograms obtained in response to 5-sec pure tones from 2-80 kc/s at 100 db SPL. Response patterns (rate-of-firing by frequency) were obtained for each rat, being greatest at frequencies below 15 kc/s. This is not the region of greatest audibility, which in the rat is thought to be 30-40 kc/s. Response latencies were determined to be 830 msec at each rat's best frequency. Evidently in rats, as in bats, the CTM is acoustically responsive, but its precise ethological role in controlling vocal pitch is not as yet understood.

Speech discrimination in children: auditory and auditory/visual processing with binaural and monaural presentation.

The Word Intelligibility by Picture Identification test was recorded with electret microphones inserted at the ear canals of a child listener. This recording paradigm has been shown to preserve binaural cues. Thirty normal-hearing children (ages 6 to 14) responded to binaural and monaural stimulation under auditory and auditory/visual presentation at six signal-to-noise (S/N) ratios (varying from +3 to -12 dB). At the higher and lower S/N ratios, the binaural advantage was minimized. For the auditory alone mode, the largest mean difference of 21% intelligibility improvement from monaural to binaural presentations occurred at -6 dB S/N, whereas in the auditory/visual mode, an intelligibility improvement of 20.8% occurred at -9 dB S/N. Implications for binaural amplification for the hearing impaired who operate on minimal residual hearing follow from the results of this study.

Masking level differences: auditory evoked responses with homophasic and antiphasic signal and noise.

Two studies were devised to determine if objective quantification of the masking level difference is possible using the auditory evoked response (AER). In the first study, click stimuli were presented under three conditions: both the stimulus and masker in phase (SoNo); stimulus in phase, masker antiphasic (SoN pi); and stimulus antiphasic with masker in phase (S pi No). In the second study 1000 Hz puretone stimuli were presented under SoNo and S pi No phasic conditions. AER's were obtained at various intensity levels for each condition. The AER demonstrated differences in N1-P2 amplitudes evoked by the homophasic and antiphasic conditions for threshold and suprathreshold levels.

Burst width tracking: brief tone thresholds in the normal ear.

This study presents a unique procedure for determining the critical duration and temporal summation function. With this procedure, duration as a parameter was used to determine the temporal summation characteristics of ten normal ears. An apparatus was constructed that permitted subjects to track threshold by modulating the burst width of a brief tonal stimulus. The apparatus permitted experimenter control of the rate of burst width modulation and interburst interval. The burst width could be continuously varied by the subject from 10 to 800 msec. Asymptotic regression indicated that the data were best fit to a simple power function of the form Y = AX(B). A logarithmic transformation was applied to the obtained durations, and slopes of integration were determined for each frequency. These values ranged between 6.3 and 10.2 dB/log unit time. Differences among frequencies were found to be significant. Critical durations were obtained for each subject, and these values were consistent with previous data indicating negligible temporal summation about 150 to 200 msec.

Classical conditioning of the stapedius muscle.

A delayed conditioning paradigm was employed to condition the stapedius muscle. While many previous attempts have failed using loud sound as the unconditioned stimulus(UCS), this paper presents evidence of successful conditioning of this muscle when the unconditioned stimulus was a mild electrocutaneous stimulation of the external ear canal. Using a weak tone as the conditioned stimulus, conditioned responses were readily obtained in eight of ten subjects after only 30 or fewer toneshock pairs. Temporal con ditioning was also demonstrated. A parallel is shown to exist between attempts to condition the pupillary and stapedius reflexes.

Eardrum displacement following stapedius muscle contraction.

Simultaneous monitoring in human subjects on the same ear of eardrum displacement by tympanomanometry, and impedance with the electroacoustic bridge, provided information concerning contraction of the stapedius muscle and its effect on eardrum displacement. Extensive control procedures were employed to elicit only the stapedius reflex; lower intensity auditory stimulation, electrocutaneous stimulation of the homolateral external ear canal, and anesthetization of nerves leading to the tensor tympani. Following these procedures the following results were obtained: (1) Extremely small biphasic and monophasic eardrum movements were seen in the stapedius--only ear to auditory and electrocutaneous stimulation; the form of the response was much less predictable to auditory stimulation. (2) At high sound intensities relatively large inward and biphasic movements of the eardrum occurred in the normal ear, unquestionably due to contraction of the tensor tympani. These results were further validated in a group of stapedectomized ears, without the stapedius but with normal tensor tympani. (3) Biphasic responses did not occur in the tensor tympani--only ear, only monophasic inward responses. (4) Upon air-jet stimulation to the orbit of the eye, these subjects had an accentuated tensor response in that large inward movements of the eardrum occurred as compared with those in normal ears, suggesting that there is an alteration of the tensor response by the presence of the stapedius muscle. Estimates of the actual eardrum displacement were calculated based on a model of the external ear canal and eardrum.