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Prospective epidemiological study of secretory otitis media in children not attending kindergarten. A prevalence study
InternationalJournalofPediatricOtorhinolaryngology, Elsevier
11 (1986) 191-197
191
POR 00372
Prospective epidemiological study of secretory otitis media in children not attending kindergarten. A prevalence study L. B i r c h a n d O. E l b r o n d Department of Otorhinolaryngology, University Hospital of Aarhus, Aarhus (Denmark) (Received May 20th, 1985) (Revised version received November 30th, 1985) (Accepted March 15th, 1986)
Key words." secretory otitis media-tympanometry-home care Summary This prevalence study of secretory otitis media (SOM) comprised 210 children who were not attending or had not attended kindergarten. The results were c o m p a r e d with those in a previous study on 373 children from 9 kindergartens and 1 day nursery in the same municipality. The prevalence peak was at one year of age in both groups, being about 40% for non-institution-care and 7070 for institution-care children. The former group showed a decrease in the prevalence from the age of 1 - 2 years, but thereafter the prevalence fell only slightly towards the age of 6. The latter group decreased evenly from the age of 1-6, but both groups ended up at about 15%. Bilateral SOM was most c o m m o n at the age of one year, but the non-institution-care children showed another peak at 5 years of age.
Introduction Secretory otitis media (SOM) has been a subject of enormous interest during the past few years. This is manifest in several comprehensive epidemiological studies based upon impedance audiometry [4,5,11,12,14,16,17], performed partly to map the prevalence and incidence of SOM in relation to age, geographic location, conditions of care and climatic conditions, partly to select children in whom there may be an indication for treatment [9,10,15].
Correspondence: L. Birch, Department of Otorhinolaryngology, University Hospital of Aarhus, Aarhus, Denmark. 0165-5876/86/$03.50 © 1986 Elsevier Science Publishers BA. (Biomedical Division)
192 In a previous investigation we have carried out prevalence/incidence calculations on SOM a m o n g 373 children from one day nursery and 9 kindergartens in the age range 9 months to 7 years. This was done by impedance audiometry [2]. In the present study prevalence calculations were done according to similar guidelines a m o n g a group of children not attending kindergartens.
Population and method In a fairly small municipality with a population of ca 17,000 a total of 709 children were not, according to information from the municipality, in kindergarten or public day care. F r o m among these children we selected, at random, 319 aged 1 - 6 years, distributed b y a b o u t 50 in each age group. The first screening test was attended by 217 of the children. At that time it was found that 7 of them had started in kindergarten, so that they were excluded from the project. Ninety-eight children were looked after exclusively at home, 52 were in private day care with up to 7 children, 11 were once a week in a playroom, and 49 were in pre-school class or school. The children in home care (98) and in private day care with up to 2 children (19) were analyzed separately, i.e. 117 out of the total series of 210. At the first visit the children had otoscopy and ordinary otological examination. During the subsequent period the children attended at 2-week i n t e r v a l s - - a total of 6 t i m e s - - a n d had tympanometry. The tympanoscope used was of the type Madsen Electronics ZS 330 with built-in writer. The middle ear pressure was measured in the range + 100 to - 3 0 0 m m H20. Compliance was given in milliliters. Thereafter, the
5045" 40" 35 30 25 I
20 L
10~
0~-0
1
2
3
4
5
6
7
Age (years)
Fig. 1. Age distribution. D, Home care/private day care (1-2 children). I~, The rest of the children.
193 ipsilateral stapedius reflex was measured twice at 1000 Hz, 105 dB SPL, with a probe tone of 85 dB SPL at 226 Hz. Jerger's [8] nomenclature was used, the A curves being traced at a pressure exceeding - 1 0 0 m m H20. The C curves were divided into C~ curves from - 1 0 0 to - 1 9 9 mm H 2 0 and C 2 curves when the middle ear pressure was less than - 1 9 9 mm H20. The B curves are usually defined on the basis of the relative gradient < 0.1 [3,13], but the tympanograms on the cards used were too small for accurate measurement. Instead, the B curve was fixed at a compliance below 0.25 ml [7]. If a stapedial reflex could be elicited, the curves were classified as the type in whose area the impedance minimum could be read. Fig. 1 presents all the children by age as well as the group in home care/private day care with not more than 2 children. There are about 30 children in each age group, but only two 7-year-olds. Most of the 5- and 6-year-old children were attending pre-school class or school, but had not previously been in kindergartens.
Results Of the 210 children originally included in the study a few dropped out, and the 6th examination was attended by only 66%. The project ran from September to December. The mean point prevalence of B curves in the total series was 20% (mean age 3.6 years), for children in home care only 18% (mean age 3.0 years), and for children in private day care with more than 2 children 24% (mean age 2.8 years). This gives no statistically significant difference, also not when correcting for age.
0
I
2
3
4
Age (years)
~
6
I
Fig. 2. Point prevalence of A rn C 1 m, C2 I~t,and B-tympanograms• %, in 1 to 7-year olds. Total series on the left. Home care/private day care (1-2 children) on the left, and the rest of the children on the right.
194 100
\ 70-
60-
u~
50-
40-
30-
'\\ \,
20-
I0-
OI
Age (years) Fig. 3. Bilateral cases of SOM in each age group (%). Bold line, home care/private day care (1-2 children); thin fine, the rest of the children.
Fig. 2 shows the percentage distribution of the mean point prevalence for A, C 1, C 2 and B curves in relation to age for the total series (on the left) and for children in h o m e care/private day care with up to 2 children (on the right). The two groups differ but little, and the B curve prevalence is at a m a x i m u m at one year of age at which it reached up to about 30%. Thereafter a statistically significant fall occurred.
100"
90"
80"
70.
60.
o
50"
40-
30-
20-
r.-/
1a-
O,
Age (years)
6
Fig. 4. Children with SOM in each age group (%). £3, Home care/private day care (1-2 children); t~, the rest of the children.
195 TABLE 1 C H A N G E S IN T H E P O I N T PREVALENCE FROM 1ST TO 6TH TEST (%) Home care/private day care (1-2 children) on the left and the rest of the children on the right. Type of tympanogram A C1 C2 B
1st test 66 17 11 6
2nd test 62 17 10 11
31 30 21 18
3rd test 20 31 22 27
35 19 24 22
4th test 16 33 25 25
44 25 16 15
5th test 35 24 23 18
36 25 23 15
6th test 25 32 16 27
24 27 20 28
21 32 19 26
From the age of 2 - 4 years it was constantly around 15%. At the age of 5 an increase was observed in children who started in pre-school class. The prevalence of C 2 curves varied only very slightly in relation to age, but yet showed a statistically significant increase from 1 to 2 years of age. Fig. 3 presents the percentage distribution of children with bilateral SOM in relation to age, for the total series and for children in home care/private care with up to 2 children. At one year of age more than half were bilateral. There was a decrease from 1 to 2 years at which only about 1 / 5 were bilateral. This was followed by another increase. When the distribution of unilateral and bilateral cases of SOM is known, the B tympanogram prevalence can be converted to the SOM prevalence in children. Fig. 4 sets out the distribution in percent of children with SOM in relation to age, for the total series and for children in home care/private day care with up to 2 children. An equalization is seen, and at one year of age about 40% have SOM. The changes that occurred from September to December may be seen from Table I. The first testing, in the middle of September, showed a low point prevalence (8%) for B curves which thereafter increased to around 20%. If the first screening, tympanometry is divided into age groups, the one-year-olds show at this time 14% B curves, converted to children having SOM (18%).
Discussion The prevalence calculation of SOM includes cases of very short duration, possibly only one day, and cases of longer duration, maybe months. Most cases can be considered a physiological condition subsiding in the course of a short time (weeks) without leaving sequelae [1]. It has previously been demonstrated that if a B curve ascertained by serial testing persists for more than 3 months, there is a great likelihood that it is going to persist longer and that the child needs treatment [6]. The main purpose of the present study was to determine the prevalence of B tympanograms in children not in municipal kindergartens or day nurseries, including those who are minded exclusively at home. At the present time, the latter group is a very small one. In the municipality under study it made up about 20% of all
196 children under 6 years of age. As mentioned above, we have previously carried out an epidemiological study of SOM in all kindergartens and day nurseries in the same municipality [2]. Although this previous study was performed at another time, also in the same year, and not concurrently with the present one (owing to capacity problems), some comparison is permissible. The present study was carried out from September until December, while the kindergarten children were studied during the period January to April, but according to exactly the same pattern. A m o n g the kindergarten children the prevalence of B curve was fairly stable at about 21-26%, while in the present study it fluctuated from 8 to 28%. Comparison of the prevalence of SOM at each year of age in the two groups shows the highest prevalence at one year of age. A m o n g the children not attending kindergarten it was about 35-40%, while among the kindergarten children it reached beyond 70%. In the group of children not attending kindergarten the SOM prevalence was fairly stable at 20-25% from the age of 2 - 4 years, falling to about 15% at 6 years. A m o n g the kindergarten children the SOM prevalence fell evenly up to the age of 6 - 7 at which it was 10-15%. As regards the distribution of unilateral and bilateral cases of SOM there was a statistically significant difference between the two groups. The m a x i m u m rate of bilateral cases was 60-70% in both groups. A m o n g day nursery children there was a peak at one year, a m o n g those who were not in institutions there were peaks at 1 and 5 years. The second peak at 5 years is explicable by closer contact with other children when they start in the pre-school class. Like other studies, the present one also revealed an increase in the prevalence in the m o n t h of September. It must be mentioned that the tympanoscope used can measure only down to - 3 0 0 m m H20, unlike the usual stationary tympanoscopes which measure right down to - 4 0 0 m m H 2 0 . This means that if the compliance reaches 0.25 ml below - 3 0 0 m m H 2 0 , without a stapedial reflex, C 2 t y m p a n o g r a m s will be classified as B tympanograms. However, this entails but little difference in the prevalence of A, C 1, C 2 and B tympanograms. The present study disclosed that the prevalence of SOM a m o n g children who have not been in day nurseries or kindergarten is high (at one year of age between 35 and 40%), but nevertheless considerably lower than in children of the same age group attending day nurseries or kindergartens. It is not definitely known whether this difference will influence the middle-ear status in these children, as there is but little difference in the prevalence of SOM a m o n g older children between those who have been and those have not been minded in day nurseries and kindergartens.
References 1 Birch, L. and Elbrond, O., Daily impedance audiometric screening of children in a day-care institution, Scand. Audiol., 14 (1985) 5-8. 2 Birch, L., Iversen, M., Elbrond, O. and Lundqvist, G.R., A prospective epidemiological investigation of secretory otitis media and tubal dysfunction in children attending day-care centers, ORL, 46 (1984) 210-216. 3 Brooks, D.N., The use of the electro-acoustic impedance bridge in the assessment of middle ear function, Int. J. Audiol., 8 (1969) 563-569.
197 4 Draper, W.L., Secretory otitis media in children. A study of 540 children, The Laryngoscope, 77 (1967) 636-653. 5 Fiellau-Nikolajsen, M., Tympanometry in three-year-old children. The 3-year follow-up of a cohort study, ORL, 43 (1981) 89-103. 6 Fiellau-Nikolajsen, M. and Lous, J., Long-term prognostic significance of serial tympanometry, ORL, 44 (1982) 90-100. 7 Haughton, P.M., Validity of tympanometry for middle ear effusions, Arch. Otolaryngol., 103 (1977) 505-513. 8 Jerger, J., Clinical experience with impedance audiometry, Arch. Otolaryngol., 92 (1970) 311-324. 9 Lildholt, T., Unilateral grommet insertion and adenoidectomy in bilateral secretory otitis media: preliminary report of the results in 91 children, Clin. Otolaryngol., 4 (1979) 87-93. 10 Lous, J., Three impedance screening programs on a cohort of seven-year-old children, Scand. Audiol., 11 (1982) 60-64. 11 Lous, J. and Fiellau-Nikolajsen, M., Epidemiology of middle ear effusion and tubal dysfunction. A one year prospective study compresing monthly tympanometry in 387 non-selected 7-year-old children, Int. J. Pediat. Otorhinolaryngol., 3 (1981) 303-317. 12 Meistrup-Larsen, K.-I., Stroyer Andersen, M., Helweg, J., Deigb.rd, J. and Peitersen, E., Variations in tympanograms in children attending group-care during a one-year period, ORL, 43 (1981) 153-163. 13 Paradise, J.L., Clyde, G.S. and Bluestone, C.D., Tympanometric detection of middle ear effusion in infants and young children, Pediatrics, 58 (1976) 198-210. 14 Poulsen, G. and Tos, M., Screening tympanometry in newborn infants and during the first six months of life, Scand. Audiol., 7 (1978) 159-166. 15 Thomsen, J. and Tos, M., Spontaneous improvement of secretory otitis, Acta Otolaryngol., 92 (1981) 493-499. 16 Tos, M., Holm-Jensen, S., Stangerup, S.E. and Hjort Sorensen, C., Changes in point prevalence of secretory otitis in pre-school children, ORL, 45 (1983) 226-234. 17 Tos, M., Poulsen, G. and Borch, J., Tympanometry in two-year-old children, ORL, 40 (1978) 206-215.
11 (1986) 191-197
191
POR 00372
Prospective epidemiological study of secretory otitis media in children not attending kindergarten. A prevalence study L. B i r c h a n d O. E l b r o n d Department of Otorhinolaryngology, University Hospital of Aarhus, Aarhus (Denmark) (Received May 20th, 1985) (Revised version received November 30th, 1985) (Accepted March 15th, 1986)
Key words." secretory otitis media-tympanometry-home care Summary This prevalence study of secretory otitis media (SOM) comprised 210 children who were not attending or had not attended kindergarten. The results were c o m p a r e d with those in a previous study on 373 children from 9 kindergartens and 1 day nursery in the same municipality. The prevalence peak was at one year of age in both groups, being about 40% for non-institution-care and 7070 for institution-care children. The former group showed a decrease in the prevalence from the age of 1 - 2 years, but thereafter the prevalence fell only slightly towards the age of 6. The latter group decreased evenly from the age of 1-6, but both groups ended up at about 15%. Bilateral SOM was most c o m m o n at the age of one year, but the non-institution-care children showed another peak at 5 years of age.
Introduction Secretory otitis media (SOM) has been a subject of enormous interest during the past few years. This is manifest in several comprehensive epidemiological studies based upon impedance audiometry [4,5,11,12,14,16,17], performed partly to map the prevalence and incidence of SOM in relation to age, geographic location, conditions of care and climatic conditions, partly to select children in whom there may be an indication for treatment [9,10,15].
Correspondence: L. Birch, Department of Otorhinolaryngology, University Hospital of Aarhus, Aarhus, Denmark. 0165-5876/86/$03.50 © 1986 Elsevier Science Publishers BA. (Biomedical Division)
192 In a previous investigation we have carried out prevalence/incidence calculations on SOM a m o n g 373 children from one day nursery and 9 kindergartens in the age range 9 months to 7 years. This was done by impedance audiometry [2]. In the present study prevalence calculations were done according to similar guidelines a m o n g a group of children not attending kindergartens.
Population and method In a fairly small municipality with a population of ca 17,000 a total of 709 children were not, according to information from the municipality, in kindergarten or public day care. F r o m among these children we selected, at random, 319 aged 1 - 6 years, distributed b y a b o u t 50 in each age group. The first screening test was attended by 217 of the children. At that time it was found that 7 of them had started in kindergarten, so that they were excluded from the project. Ninety-eight children were looked after exclusively at home, 52 were in private day care with up to 7 children, 11 were once a week in a playroom, and 49 were in pre-school class or school. The children in home care (98) and in private day care with up to 2 children (19) were analyzed separately, i.e. 117 out of the total series of 210. At the first visit the children had otoscopy and ordinary otological examination. During the subsequent period the children attended at 2-week i n t e r v a l s - - a total of 6 t i m e s - - a n d had tympanometry. The tympanoscope used was of the type Madsen Electronics ZS 330 with built-in writer. The middle ear pressure was measured in the range + 100 to - 3 0 0 m m H20. Compliance was given in milliliters. Thereafter, the
5045" 40" 35 30 25 I
20 L
10~
0~-0
1
2
3
4
5
6
7
Age (years)
Fig. 1. Age distribution. D, Home care/private day care (1-2 children). I~, The rest of the children.
193 ipsilateral stapedius reflex was measured twice at 1000 Hz, 105 dB SPL, with a probe tone of 85 dB SPL at 226 Hz. Jerger's [8] nomenclature was used, the A curves being traced at a pressure exceeding - 1 0 0 m m H20. The C curves were divided into C~ curves from - 1 0 0 to - 1 9 9 mm H 2 0 and C 2 curves when the middle ear pressure was less than - 1 9 9 mm H20. The B curves are usually defined on the basis of the relative gradient < 0.1 [3,13], but the tympanograms on the cards used were too small for accurate measurement. Instead, the B curve was fixed at a compliance below 0.25 ml [7]. If a stapedial reflex could be elicited, the curves were classified as the type in whose area the impedance minimum could be read. Fig. 1 presents all the children by age as well as the group in home care/private day care with not more than 2 children. There are about 30 children in each age group, but only two 7-year-olds. Most of the 5- and 6-year-old children were attending pre-school class or school, but had not previously been in kindergartens.
Results Of the 210 children originally included in the study a few dropped out, and the 6th examination was attended by only 66%. The project ran from September to December. The mean point prevalence of B curves in the total series was 20% (mean age 3.6 years), for children in home care only 18% (mean age 3.0 years), and for children in private day care with more than 2 children 24% (mean age 2.8 years). This gives no statistically significant difference, also not when correcting for age.
0
I
2
3
4
Age (years)
~
6
I
Fig. 2. Point prevalence of A rn C 1 m, C2 I~t,and B-tympanograms• %, in 1 to 7-year olds. Total series on the left. Home care/private day care (1-2 children) on the left, and the rest of the children on the right.
194 100
\ 70-
60-
u~
50-
40-
30-
'\\ \,
20-
I0-
OI
Age (years) Fig. 3. Bilateral cases of SOM in each age group (%). Bold line, home care/private day care (1-2 children); thin fine, the rest of the children.
Fig. 2 shows the percentage distribution of the mean point prevalence for A, C 1, C 2 and B curves in relation to age for the total series (on the left) and for children in h o m e care/private day care with up to 2 children (on the right). The two groups differ but little, and the B curve prevalence is at a m a x i m u m at one year of age at which it reached up to about 30%. Thereafter a statistically significant fall occurred.
100"
90"
80"
70.
60.
o
50"
40-
30-
20-
r.-/
1a-
O,
Age (years)
6
Fig. 4. Children with SOM in each age group (%). £3, Home care/private day care (1-2 children); t~, the rest of the children.
195 TABLE 1 C H A N G E S IN T H E P O I N T PREVALENCE FROM 1ST TO 6TH TEST (%) Home care/private day care (1-2 children) on the left and the rest of the children on the right. Type of tympanogram A C1 C2 B
1st test 66 17 11 6
2nd test 62 17 10 11
31 30 21 18
3rd test 20 31 22 27
35 19 24 22
4th test 16 33 25 25
44 25 16 15
5th test 35 24 23 18
36 25 23 15
6th test 25 32 16 27
24 27 20 28
21 32 19 26
From the age of 2 - 4 years it was constantly around 15%. At the age of 5 an increase was observed in children who started in pre-school class. The prevalence of C 2 curves varied only very slightly in relation to age, but yet showed a statistically significant increase from 1 to 2 years of age. Fig. 3 presents the percentage distribution of children with bilateral SOM in relation to age, for the total series and for children in home care/private care with up to 2 children. At one year of age more than half were bilateral. There was a decrease from 1 to 2 years at which only about 1 / 5 were bilateral. This was followed by another increase. When the distribution of unilateral and bilateral cases of SOM is known, the B tympanogram prevalence can be converted to the SOM prevalence in children. Fig. 4 sets out the distribution in percent of children with SOM in relation to age, for the total series and for children in home care/private day care with up to 2 children. An equalization is seen, and at one year of age about 40% have SOM. The changes that occurred from September to December may be seen from Table I. The first testing, in the middle of September, showed a low point prevalence (8%) for B curves which thereafter increased to around 20%. If the first screening, tympanometry is divided into age groups, the one-year-olds show at this time 14% B curves, converted to children having SOM (18%).
Discussion The prevalence calculation of SOM includes cases of very short duration, possibly only one day, and cases of longer duration, maybe months. Most cases can be considered a physiological condition subsiding in the course of a short time (weeks) without leaving sequelae [1]. It has previously been demonstrated that if a B curve ascertained by serial testing persists for more than 3 months, there is a great likelihood that it is going to persist longer and that the child needs treatment [6]. The main purpose of the present study was to determine the prevalence of B tympanograms in children not in municipal kindergartens or day nurseries, including those who are minded exclusively at home. At the present time, the latter group is a very small one. In the municipality under study it made up about 20% of all
196 children under 6 years of age. As mentioned above, we have previously carried out an epidemiological study of SOM in all kindergartens and day nurseries in the same municipality [2]. Although this previous study was performed at another time, also in the same year, and not concurrently with the present one (owing to capacity problems), some comparison is permissible. The present study was carried out from September until December, while the kindergarten children were studied during the period January to April, but according to exactly the same pattern. A m o n g the kindergarten children the prevalence of B curve was fairly stable at about 21-26%, while in the present study it fluctuated from 8 to 28%. Comparison of the prevalence of SOM at each year of age in the two groups shows the highest prevalence at one year of age. A m o n g the children not attending kindergarten it was about 35-40%, while among the kindergarten children it reached beyond 70%. In the group of children not attending kindergarten the SOM prevalence was fairly stable at 20-25% from the age of 2 - 4 years, falling to about 15% at 6 years. A m o n g the kindergarten children the SOM prevalence fell evenly up to the age of 6 - 7 at which it was 10-15%. As regards the distribution of unilateral and bilateral cases of SOM there was a statistically significant difference between the two groups. The m a x i m u m rate of bilateral cases was 60-70% in both groups. A m o n g day nursery children there was a peak at one year, a m o n g those who were not in institutions there were peaks at 1 and 5 years. The second peak at 5 years is explicable by closer contact with other children when they start in the pre-school class. Like other studies, the present one also revealed an increase in the prevalence in the m o n t h of September. It must be mentioned that the tympanoscope used can measure only down to - 3 0 0 m m H20, unlike the usual stationary tympanoscopes which measure right down to - 4 0 0 m m H 2 0 . This means that if the compliance reaches 0.25 ml below - 3 0 0 m m H 2 0 , without a stapedial reflex, C 2 t y m p a n o g r a m s will be classified as B tympanograms. However, this entails but little difference in the prevalence of A, C 1, C 2 and B tympanograms. The present study disclosed that the prevalence of SOM a m o n g children who have not been in day nurseries or kindergarten is high (at one year of age between 35 and 40%), but nevertheless considerably lower than in children of the same age group attending day nurseries or kindergartens. It is not definitely known whether this difference will influence the middle-ear status in these children, as there is but little difference in the prevalence of SOM a m o n g older children between those who have been and those have not been minded in day nurseries and kindergartens.
References 1 Birch, L. and Elbrond, O., Daily impedance audiometric screening of children in a day-care institution, Scand. Audiol., 14 (1985) 5-8. 2 Birch, L., Iversen, M., Elbrond, O. and Lundqvist, G.R., A prospective epidemiological investigation of secretory otitis media and tubal dysfunction in children attending day-care centers, ORL, 46 (1984) 210-216. 3 Brooks, D.N., The use of the electro-acoustic impedance bridge in the assessment of middle ear function, Int. J. Audiol., 8 (1969) 563-569.
197 4 Draper, W.L., Secretory otitis media in children. A study of 540 children, The Laryngoscope, 77 (1967) 636-653. 5 Fiellau-Nikolajsen, M., Tympanometry in three-year-old children. The 3-year follow-up of a cohort study, ORL, 43 (1981) 89-103. 6 Fiellau-Nikolajsen, M. and Lous, J., Long-term prognostic significance of serial tympanometry, ORL, 44 (1982) 90-100. 7 Haughton, P.M., Validity of tympanometry for middle ear effusions, Arch. Otolaryngol., 103 (1977) 505-513. 8 Jerger, J., Clinical experience with impedance audiometry, Arch. Otolaryngol., 92 (1970) 311-324. 9 Lildholt, T., Unilateral grommet insertion and adenoidectomy in bilateral secretory otitis media: preliminary report of the results in 91 children, Clin. Otolaryngol., 4 (1979) 87-93. 10 Lous, J., Three impedance screening programs on a cohort of seven-year-old children, Scand. Audiol., 11 (1982) 60-64. 11 Lous, J. and Fiellau-Nikolajsen, M., Epidemiology of middle ear effusion and tubal dysfunction. A one year prospective study compresing monthly tympanometry in 387 non-selected 7-year-old children, Int. J. Pediat. Otorhinolaryngol., 3 (1981) 303-317. 12 Meistrup-Larsen, K.-I., Stroyer Andersen, M., Helweg, J., Deigb.rd, J. and Peitersen, E., Variations in tympanograms in children attending group-care during a one-year period, ORL, 43 (1981) 153-163. 13 Paradise, J.L., Clyde, G.S. and Bluestone, C.D., Tympanometric detection of middle ear effusion in infants and young children, Pediatrics, 58 (1976) 198-210. 14 Poulsen, G. and Tos, M., Screening tympanometry in newborn infants and during the first six months of life, Scand. Audiol., 7 (1978) 159-166. 15 Thomsen, J. and Tos, M., Spontaneous improvement of secretory otitis, Acta Otolaryngol., 92 (1981) 493-499. 16 Tos, M., Holm-Jensen, S., Stangerup, S.E. and Hjort Sorensen, C., Changes in point prevalence of secretory otitis in pre-school children, ORL, 45 (1983) 226-234. 17 Tos, M., Poulsen, G. and Borch, J., Tympanometry in two-year-old children, ORL, 40 (1978) 206-215.