Risk factors and confounders in the geographical clustering of schizophrenia

In response to previous reports of geographical clustering of individuals with psychosis, a study was carried out in Denmark utilizing the national case register. Two-thousand one-hundred and ninety-nine (2199) individuals with schizophrenia were divided by place of birth into 217 geographical areas and analyzed by age, gender, month of birth, genetic relatedness, and degree of urbanization of birthplace. Heterogeneity was ascertained using log-linear Poisson regression. The greatest amount of heterogeneity was associated with degree of urbanization of place of birth. Heterogeneity was also associated with age-gender interaction and calendar period. When adjusted for these factors, there was no remaining heterogeneity, suggesting that all geographical clustering in our study was explained by the above factors.

The role of chaperone-assisted folding and quality control in inborn errors of metabolism: protein folding disorders

Molecular chaperones are present in the various compartments of the cell and assist the folding of newly synthesized proteins. Compared to wild-type proteins, missense mutant proteins are generally synthesized in a normal fashion, but may be impaired in their folding. A broad array of diseases that are due to misfolding of mutant proteins may be labelled conformational diseases: aggregation diseases, such as Alzheimer disease; diseases caused by negative dominance from misfolded structural proteins, such as hypertrophic cardiomyopathy; and disorders where the misfolded protein is degraded by intracellular proteases. Many metabolic disorders belong to this last category, where the so-called protein quality control systems, comprising chaperones and proteases, attempt to eliminate folding intermediates or misfolded proteins. On the basis of in vitro experiments with a limited number of missense mutations identified in patients with phenylalanine hydroxylase and fatty acid oxidation deficiencies, we discuss the cellular fate of missense mutant proteins. We find that the balance between folding to functional conformers, retention (holding) and degradation of folding intermediates or misfolded proteins is dependent on the nature of the mutation and on the efficiency of the quality control. For example, low temperature may promote formation of functional conformers, while elevated temperature usually promotes retention and degradation. We conclude that disorders caused by many missense mutations are complex diseases in which the mutation itself is a necessary major primary component, but that its effect may be modified by cellular conditions and possibly by genetic variations in the quality control systems. We suggest that this new knowledge about cell handling may open new avenues of understanding of the cell pathology and treatment of patients with metabolic disorders.

Fiber-optic probe for noninvasive real-time determination of tissue optical properties at multiple wavelengths

We present a compact, fast, and versatile fiber-optic probe system for real-time determination of tissue optical properties from spatially resolved continuous-wave diffuse reflectance measurements. The system collects one set of reflectance data from six source-detector distances at four arbitrary wavelengths with a maximum overall sampling rate of 100 Hz. Multivariate calibration techniques based on two-dimensional polynomial fitting are employed to extract and display the absorption and reduced scattering coefficients in real-time mode. The four wavelengths of the current configuration are 660, 785, 805, and 974 nm, respectively. Cross-validation tests on a 6 x 7 calibration matrix of Intralipid-dye phantoms showed that the mean prediction error at, e.g., 785 nm was 2.8% for the absorption coefficient and 1.3% for the reduced scattering coefficient. The errors are relative to the range of the optical properties of the phantoms at 785 nm, which were 0-0.3/cm for the absorption coefficient and 6-16/cm for the reduced scattering coefficient. Finally, we also present and discuss results from preliminary skin tissue measurements.

Acute mastoidectomy in a Danish county from 1977 to 1997--operative findings and long-term results

Data from patients undergoing acute mastoidectomy were examined retrospectively to evaluate if the nature of acute mastoiditis (AM) treated surgically has changed during the last 20 years (1977-97). Moreover, a prevalence study was conducted to clarify the otological and audiological course following acute mastoidectomy. Patients with cholesteatoma and intracranial complications were excluded. Thus, 79 patients with a median age of 16 months were included. Thirty-seven percent had a history of middle ear disease, and the mean duration from onset of symptoms to admission was 9 days. Well-being was affected in 46%, and 82% had fever. The clinical picture was dominated by auricular protrusion (77%) and pathological tympanic membrane (94%). Postauricular oedema, hyperaemia and tenderness were demonstrated in 89%, 78% and 49% of cases, respectively. Peroperatively, purulent middle ear effusion was recognized in 92%, subperiosteal abscess in 66% and pus in the mastoid in 90%. Specimens revealed growth of pathogens in 58%, predominantly Gram-positive bacteria. The observation period was 1-20 years. The findings in operated ears were not significantly different from the contralateral non-operated ears concerning incidence of otitis media, hearing and ear canal volume. Conclusively, acute mastoidectomy is a safe and effective treatment to eliminate infection. The operation can be done with negligible risk and does not leave long-term sequelae.

Middle ear epithelium has inflammatory capacity

Endotoxin, tumour necrosis factor-alpha (TNF-alpha), interleukin-1 beta (IL-1 beta) and intercellular adhesion molecule-1 (ICAM-1) were detected in 88%, 51%, 58% and 66% of 152 middle ears from patients suffering from otitis media with effusion. In this study the hypothesis that bacterial endotoxin, TNF-alpha, IL-1 beta and ICAM-1 induce the inflammatory process characteristic of otitis media with effusion was tested. Cultures of rabbit middle ear epithelium were exposed to endotoxin, TNF-alpha or IL-1 beta. The expression of ICAM-1 on the cell surfaces was measured with a direct enzyme-linked immunosorbent assay on the cell layer. For TNF-alpha, 5 ng/ml significantly increased ICAM-1 expression, whereas 100 ng/ml had a toxic effect. For IL-1 beta, as little as 1 ng/ml produced a significant increase in ICAM-1 expression. Endotoxin stimulated ICAM-1 expression less strongly in concentrations from 100 ng/ml to 100 micrograms/ml. The findings indicate that stimulation of ICAM-1 by endotoxin is mediated, at least in part, by TNF-alpha and IL-1 beta. It is concluded that endotoxin induces sustained inflammation in OME, and that this inflammation is mediated, at least in part, by the primary cytokines TNF-alpha and IL-1 beta.

Results and experience of 50 cochlear implant operations

Cochlear implantation (CI) is a relatively new type of treatment that aims to re-establish hearing in deaf people. This paper reports on the results from CI operations on 34 adults and 17 children. All patients benefited from the treatment. The adults' communication with other people improved. Almost all patients use their implant 16 h a day and some of them are able to communicate by telephone. Among children the results show that the treatment is safe, as no complications have developed. Hearing and speech improved in all children, and thus also their ability to communicate. The results obtained are dependent on the individual patient's condition, the time of operation in relation to the development of deafness, and the type of CI used. CI treatment of deaf people may be considered to be one of the greatest advances in otology.

Cortical networks subserving the perception of tinnitus--a PET study

Subjective tinnitus is an auditory phantom perception that may arise from any aberrant signal within the auditory system. Further processing of this signal and the conscious perception of tinnitus takes place in the cerebral cortex. A few functional brain-imaging studies have been performed to elucidate the underlying cerebral mechanisms of this perception. These studies mostly concern rare types of tinnitus (e.g. tinnitus changeable by oral-facial movements), or compared tinnitus patients with healthy volunteers. These studies attributed variable activation of the primary auditory cortices, associative auditory cortices and the left hippocampus to the perception of tinnitus. Based on these heterogeneous results, no consensus on the underlying mechanisms has been reached. The aim of the present study was to obtain further details of the central perception and processing of the tinnitus signal. Positron emission tomography (PET) was used to map the tinnitus-specific central activity. By contrasting PET-images of suppressed tinnitus with PET-images of the habitual tinnitus sensation, we were able to identify a right prefrontal-temporal network associated with the perception of tinnitus. Besides the evidence of activation of associative auditory sensory regions, the results indicated that activation of cortical centres subserving attention and emotion may underlie the continuous irritability associated with severe tinnitus.

Incidence and growth pattern of vestibular schwannomas in a Danish county, 1977-98

During a period of 21 years 162 acoustic neuromas or vestibular schwannomas (VS) were diagnosed in the county of Aarhus. During this period the incidence increased gradually, probably due to improvement of the quality of computed tomography imaging (CTI), and more widely available access to magnetic resonance imaging (MRI). Sixty-four patients were followed up by repeated CTI or MRI, whereas the remaining patients were referred for immediate operation. Six of the observed patients had their tumours removed after demonstration of continuous tumour growth. The observation of 64 tumours over periods between 5 months and 15 years provided useful information on the natural history of sporadic VS. Our results showed that 14 VS (22%) regressed, 35 VS (55%) did not grow or had only minimal growth (growth rate up to 1 mm/year), whereas 15 VS (23%) grew > 1 mm/year. All VS with positive growth had regular growth patterns.

How does endotoxin trigger inflammation in otitis media with effusion?

OBJECTIVES

The relationship among microorganisms, endotoxin, and inflammatory mediators in otitis media with effusion (OME) was examined.

STUDY DESIGN

Analysis of 152 middle ear effusions aspirated at the time of ventilation tube insertion from children with OME.

METHODS

Effusion samples were cultured for pathogenic bacteria The two primary cytokines, interleukin-1beta (IL1beta) and tumor necrosis factor (TNFalpha), and the adhesion molecules, intercellular and vascular adhesion molecule (ICAM-1 and VCAM-1), were quantified using the enzyme-linked immunosorbent assay (ELISA) technique. Endotoxin concentration was measured with a limulus amebocyte lysate assay, and total protein concentration was quantified using the Biorad microassay.

RESULTS

The cultures of pathogenic bacteria were positive in 33 of the 152 effusions (22%), which contained more endotoxin and more of the primary cytokines than the 119 culture-negative effusions. Endotoxin and the primary cytokines were positively correlated, both in the whole material and in the sterile effusions alone. The adhesion molecules were positively correlated with each other, but not with endotoxin or the primary cytokines.

CONCLUSIONS

We found a positive correlation between endotoxin and the primary cytokines TNFalpha and IL1beta in culture-positive OME effusions as well as in culture-negative ones, suggesting endotoxin-induced local production of TNFalpha and IL1beta in the middle ear. ICAM-1 and VCAM-1 were also present in the middle ear, but their concentrations were not directly correlated to endotoxin or the primary cytokines.

[Results and experiences with 55 cochlear implantations]

INTRODUCTION

The etiology of deafness in deaf people is defects in the cochlea hair cells. Cochlear implant treatment gives deaf born and patients with acquired deafness the possibility to reestablish or obtain hearing by electric stimulation of the cochlear nerve. In this paper the results of treatment of 35 adults and 20 children are reported.

METHOD

The candidates for cochlear implant treatment are extensively investigated before the decision is made to operate. The operative treatment takes place under general anaesthesia and the operative technique is outlined. In the treatment of the deaf, different types of implants and stimulation strategies have been used. The effect of treatment is considered by hearing test and evaluation of speech.

RESULTS

Nine of the adults obtained a hearing quality that made using a telephone possible. Almost all adults can by the combination of cochlear implant and lip reading perform a normal conversation. The results in the deaf born children are obtained slowly as the deaf born have to develop hearing and speech from zero. All the treated children have improved possibilities of communication.

DISCUSSION

Cochlear implant treatment of deaf people now seems well established both internationally and nationally in Denmark. Cochlear implant equipment has improved considerably throughout the past years and that it today is possible to establish hearing in deaf born or patients with acquired deafness can be considered as one of the greatest developments in otology, maybe the greatest.

[Treatment of tinnitus with low-intensity laser]

This study evaluated the effect of low-power laser in the treatment of tinnitus in a randomized, prospective, double-blind, placebo-controlled trial. The active laser applied 50 mW (cw, 830 nm) over a period of 10 minutes per session. Forty-nine patients were included. The main outcome was measured using psychoacoustical match of tinnitus loudness, Visual Analog Scale (VAS) ratings of subjective loudness, annoyance and attention involved, scores on tinnitus-specific questionnaires, and a number of psychosocial questionnaires. Only few subjects (18%) experienced subjective improvement. There were no statistically significant differences between the effects of the active laser and placebo treatments.

CONCLUSION

Low-power laser treatment is not indicated in the treatment of tinnitus. Reports of significant benefits of this treatment in previous studies may be explained by the placebo effect.

[Meniere's disease. The clinical effect of gentamicin treatment]

In patients with Menière's disease attacks of vertigo can be invalidating. We have tested the effect of instillation of gentamycin in the middle ear to minimize or stop the attacks of vertigo. The results of a prospective investigation of 14 patients with Menière's disease treated with gentamycin in the period from 1993 to 1996 are presented. The patients were followed up to 53 months after the treatment and a telephone follow-up was performed. At the last follow-up nine out of 12 patients were free of attacks of vertigo. Two improved and one patient was unchanged. In two patients deafness developed in the treated ear, in the other patients the hearing was unchanged measured by speech reception threshold and discrimination loss. It is concluded that treatment of patients with Menière's disease by instillation of gentamycin into the middle ear does have a therapeutic effect. The treatment is simple and the effect of treatment is equal to other types of treatments. The risk of deafness in the treated ears stresses the importance of giving the patient sufficient information before treatment.

Effects of blueberry and cranberry juice consumption on the plasma antioxidant capacity of healthy female volunteers

OBJECTIVE

To assess whether consumption of 500 ml of blueberry juice or cranberry juice by healthy female subjects increased plasma phenolic content and antioxidant capacity.

DESIGN

Latin square arrangement to eliminate ordering effects. After an overnight fast, nine volunteers consumed 500 ml of blueberry juice, cranberry juice or a sucrose solution (control); each volunteer participated on three occasions one week apart, consuming one of the beverages each time. Blood samples were obtained by venipuncture at intervals up to four hours after consumption of the juices. Urine samples were also obtained four hours after consuming the juice.

RESULTS

Consumption of cranberry juice resulted in a significant increase in the ability of plasma to reduce potassium nitrosodisulphonate and Fe(III)-2,4, 6-Tri(2-pyridyl)-s-triazine, these measures of antioxidant capacity attaining a maximum after 60-120 min. This corresponded to a 30% increase in vitamin C and a small but significant increase in total phenols in plasma. Consumption of blueberry juice had no such effects.

CONCLUSION

The increase in plasma antioxidant capacity following consumption of cranberry juice could mainly be accounted for by an increase in vitamin C rather than phenolics. This also accounted for the lack of an effect of the phenolic-rich but vitamin C-low blueberry juice.

SPONSORSHIP

Funded by the Scottish Executive Rural Affairs Department and the Danish Government.

Pseudoaneurysm of a lateral internal carotid artery in the middle ear

We report a case where a 7-year-old girl suffered significant aural bleeding following myringotomy of the tympanic membrane. Investigations by computed tomography scan, carotid angiography, and magnetic resonance angiography showed a lateral aberrant internal carotid artery (LACI) with a little pseudoaneurysm in the middle ear. The anomaly of the internal carotid artery was supposed to be congenital, and the pseudoaneurysm was supposed to be traumatic, formed after incision into the wall of the artery. Considerations about diagnosis, symptoms, and treatment are discussed. The patient was treated by balloon embolization in the internal carotid artery without sequelae.

Reliability and validity of a Danish adaptation of the Tinnitus Handicap Inventory

The objective of this study was to determine the reliability and validity of a Danish translation of the Tinnitus Handicap Inventory (THI), a self-report measure of perceived tinnitus handicap. The Danish version of the THI was administered to 50 patients reporting tinnitus as their primary complaint or secondary to hearing loss. Construct validity was assessed using tinnitus symptom rating scales, the Beck Depression Inventory (BDI), the State-Trait Anxiety Inventory (STAI), the Tinnitus Coping Style Questionnaire (TCSQ), the Eysenck Personality Questionnaire (EPQ), and perceived tinnitus loudness and pitch. The Danish translation of the THI and its subscales showed good internal consistency reliabilities (c = 0.93 to alpha = 0.74) comparable to those of the original version. High to moderate correlations were observed between THI and psychological distress, tinnitus symptom ratings, neuroticism and maladaptive tinnitus coping. A confirmatory factor analysis failed to validate the three subscales of THI, and high intercorrelations found between the subscales question whether they represent three distinct factors. The results suggest that the Danish THI-Total scale may be a reliable and valid measure of general tinnitus related distress that can be used in a clinical setting to quantify the impact of tinnitus on daily living.

Functional brain imaging of tinnitus-like perception induced by aversive auditory stimuli

Tinnitus is an aversive auditory percept of unknown origin. We tested the speculation that tinnitus may share neuronal processing mechanisms with aversive auditory percepts of known origin. This study revealed the functional neuroanatomy of the perception of aversive auditory stimuli. The stimuli were presented to 12 healthy volunteers so as to mimic the psychoacoustical features of tinnitus and its affective response in tinnitus sufferers. The regional cerebral blood flow distribution was measured by PET during four auditory processing conditions and one control condition. The aversive auditory stimuli activated primary and secondary auditory areas bilaterally, dorsolateral prefrontal attention areas, and structures in the limbic system which subserve emotional processing. Based on these results and findings from other functional neuroimages of tinnitus, we hypothesize that the perception of tinnitus may involve the functional linkage of these brain areas: secondary auditory cortex, dorsolateral prefrontal cortex, and limbic system.

Cortical centres underlying auditory temporal processing in humans: a PET study

We have used positron emission tomography (PET) to test a specific hypothesis of a neural system subserving auditory temporal processing (acoustical stimulus duration discrimination). Maps of the cerebral blood flow distribution during specific stimulations were obtained from five normally-hearing and otherwise healthy subjects. The auditory stimuli consisted of sounds of varying duration and of auditorily presented words in which the duration of the initial phoneme was manipulated. All stimuli alternated with conditions of silence in a subtraction paradigm. The blood flow distribution was mapped with O-15-labelled water. The results demonstrated that stimuli requiring recognizing, memorizing, or attending to specific target sounds during temporal processing generally resulted in significant activation of both frontal lobes and the parietal lobe in the right hemisphere. Based on these results, we hypothesise that a network consisting of anterior and posterior auditory attention and short-term memory sites subserves acoustical stimulus duration perception and analysis (auditory temporal processing).

Exposure to prenatal and childhood infections and the risk of schizophrenia: suggestions from a study of sibship characteristics and influenza prevalence

BACKGROUND

It has been proposed that infections, perhaps prenatal exposure to the influenza virus, might increase the risk of schizophrenia. To address this hypothesis, we studied the possible influence on schizophrenia risk of sibship characteristics and ecological influenza prevalence data. Birth order and influenza prevalence were used as proxy measures for exposure to prenatal infection, and sibship size and interval to siblings were used as proxy measures for exposure to common childhood infections.

METHODS

We established a population-based cohort of 1746366 persons whose mothers were Danish-born women born since 1935 by using data from the Civil Registration System. Schizophrenia in cohort members (n = 2669) and their parents was identified by linkage with the Danish Psychiatric Case Register. Birth order, sibship size, and interval to siblings were calculated for each cohort member based on person-identifiable information on all siblings. The number of notifications of influenza per month in Denmark was obtained from the National Board of Health and Statens Serum Institut.

RESULTS

There was no association between birth order and schizophrenia risk or between schizophrenia risk and influenza prevalence during any month of prenatal life. Coming from a large sibship was associated with an increased schizophrenia risk. The relative risks were 1.26 (95% confidence interval [CI], 1.11-1.44) and 1.46 (95% CI, 1.22-1.75) for sibships of 4 and 5 or more, respectively, vs. a sibship of 2. Short interval (<2 years) to the nearest older sibling and nearest younger sibling was associated with a risk of 1.22 (95% CI, 1.05-1.38) and 1.15 (95% CI, 1.03-1.28), respectively, compared with longer intervals.

CONCLUSIONS

Our findings do not support the hypothesis that schizophrenia is associated with prenatal exposure to common infections or influenza. However, they are compatible with the hypothesis that environmental exposure, perhaps to common infections in childhood, may be a risk factor, although other explanations are also possible.

Stimulus-dependent central processing of auditory stimuli: a PET study

Positron emission tomography (PET) was used to investigate the neural systems involved in the central processing of different auditory stimuli. Noise, pure tone and pure-tone pulses, music and speech were presented monaurally. O-15-water PET scans were obtained in relation to these stimulations presented to five normal hearing and healthy subjects. All stimuli were related to a basic scan in silence. Processing of simple auditory stimuli, such as pure tones and noise, predominantly activate the left transverse temporal gyrus (Brodmann area [BA] 41), whereas sounds with discontinued acoustic patterns, such as pure-tone pulse trains, activated parts of the auditory association area in the superior temporal gyri (BA 42) in both hemispheres. Moreover, sounds with complex spectral, intensity, and temporal structures (words, speech, music) activated spatially even more extensive associative auditory areas in both hemispheres (BA 21, 22). PET has revealed a remarkable potential to investigate early central auditory processing, and has provided evidence of the coexistence of functionally linked, but individually active parallel and serial auditory networks.

The low-power laser in the treatment of tinnitus

The purpose of this study was to evaluate the low-power laser on the treatment of tinnitus. In a randomized, prospective, double-blind, placebo-controlled trial, either active or placebo low-power laser irradiation was given through the external acoustic meatus of the affected ear towards the cochlea. The active laser applied 50 mW (cw, 830 nm) over a period of 10 min per session. Forty-nine patients with severe, chronic uni- or bilateral tinnitus were studied. The main outcome was measured using psychoacoustical match of tinnitus loudness and pitch, Visual Analogue Scale (VAS) ratings of subjective loudness, annoyance and attention involved, scores on the Tinnitus Handicap Inventory (THI), the Tinnitus Coping Style Questionnaire (TCSQ), and a number of psychosocial questionnaires. The results showed only moderate (18%) subjective improvement with no statistically significant differences between the effects of the active laser and placebo treatments. Also, there were no statistically significant differences in prepost measurements of tinnitus loudness, VAS scores, THI scores, or TCSQ scores for patients treated with active laser compared with those treated with placebo. We conclude that low-power laser treatment is not indicated in the treatment of tinnitus. Reports of significant benefits of this treatment in previous, mostly uncontrolled or single-blinded studies may be explained by the placebo effect.

Laser stapedotomy

Thirty-four ears with conductive hearing loss due to otosclerosis were operated upon using the laser stapedotomy technique. Audiological results were compared with the results of 316 non-laser stapedotomies. The post-operative air-bone gap, calculated as the difference between the post-operative air and bone conduction levels, was smaller with the laser stapedotomy group. Also, the bone conduction showed significant improvement with the use of laser. Significant sensorineural hearing loss was not found in any of the laser-treated patients. According to our results, we concluded that laser is of benefit in stapes surgery for improving the hearing results and minimizing the inner ear trauma.

Stapedotomy: does prosthesis diameter affect outcome?

Two hundred ears with otosclerosis have been operated upon using a 0.4-mm diameter Teflon platinum piston in 100 ears and a 0.6-mm diameter Teflon piston in the other 100 ears. The postoperative air-bone gap, calculated as the difference between the postoperative air and bone conduction levels, was smaller in the 0.6 mm group for all frequencies except at 2000 Hz, the differences were statistically insignificant except at 4000 Hz. The mean postoperative air-bone gap was 8.6 dB and 7.4 dB for the 0.4 and 0.6 mm groups, respectively, which is statistically insignificant. We found no postoperative loss of bone conduction exceeding 15 dB, there was a deterioration of more than 10 dB in three ears, one in the 0.4 mm group and two in the 0.6 mm group. According to our results, we conclude that the 0.4 mm and the 0.6 mm Teflon prostheses produce the same hearing improvement in stapes surgery for otosclerosis.

Risk factors for parvovirus B19 infection in pregnancy

CONTEXT

Parvovirus B19 infection during pregnancy has been associated with fetal death. However, the incidence of and risk factors for infection in pregnant women have not been well studied.

OBJECTIVES

To estimate a pregnant woman's risk of infection with parvovirus B19 in epidemic and endemic situations and to study risk factors for infection.

DESIGN

Population-based cohort study conducted between November 1992 and June 1994.

SETTING

Three regions in Denmark.

PARTICIPANTS

A total of 30946 pregnant women from a consecutive and population-based screening.

MAIN OUTCOME MEASURES

Specific IgG antibodies in serum samples obtained in the first trimester of pregnancy and from the newborn infant to assess past infection and seroconversion. Information on family structure, educational background, socioeconomic status, and pregnancy outcome was obtained from national registers.

RESULTS

Based on 30 946 serum samples, 65.0% of pregnant women had evidence of past infection. Annual seroconversion rates among susceptible women during endemic and epidemic periods were 1.5% (95% confidence interval [CI], 0.2%-1.9%) and 13.0% (95% CI, 8.7%-23.1 %), respectively. Baseline seropositivity was significantly correlated with increasing number of siblings, having a sibling of the same age, number of own children, and occupational exposure to children. Risk of acute infection increased with the number of children in the household as follows: 0 children odds ratio (OR), 1 (reference); 1 child OR, 3.17 (95% CI, 2.24-4.49); 2 children OR, 5.47 (95% CI, 3.55-8.45); 3 or more children OR, 7.54 (95% CI, 3.80-14.94). Having children aged 6 to 7 years resulted in the highest rate of seroconversion among mothers (6.8%; OR, 4.07; 95% CI, 1.89-8.73). Compared with other pregnant women, nursery school teachers had a 3-fold increased risk of acute infection (OR, 3.09; 95% CI, 1.62-5.89). Population-attributable risk of seroconversion was 55.4% for number of own children and 6.0% for occupational exposure.

CONCLUSIONS

The risk of infection is high for susceptible pregnant women during epidemics and associated with the level of contact with children. Nursery school teachers have the highest occupational risk, but most infections seem to be the result of exposure to the woman's own children.