- Email: [email protected]
Antibodies against Borrelia burgdorferi in bavarian forest workers
Zbl. Bakt . Hyg. A 26 3,412-41 9 (1986)
Antibodies against Borrelia burgdorferi in Bavarian Forest Workers PETER MUNCHHOFF 2 , BETTINA WILSKE 1 , VERA PREA C-MURSIC I , and GUNTER SCHIERZ 1 . I M ax von Pett enkofer-Institut fur Hygiene und Medizinische Mikro biologie der Ludwig Maxirnilians-Universirat Mii nchen, FRG Direktor : Pro f. Dr. F. Deinhardt 2 Beru fsgenossenschaftl icher Arbeitsme dizin ischer Dienst, Zentrum Mii nchen, FRG
Summary The sera of 496 forest workers (fw), 44 custo ms officials and 20 other person s in outdoor profession s from different areas of Bavaria were tested for anti bodies against Borrelia burgdorferi (strain B 31) by indirect immuno fluo rescence. In sera previously abso rbed with Treponema pbagedenis ultr asoni cate, significan tly elevated IgG antibody titers were found in 69 cases, in 68 fw (13,7%) and 1 custom agent . In accor dance with previous observations the distributi on of pos itive results show ed a distin ct age dependan ce: under 24 years (y) 1.6% (n = 64),25-34 y 0 (n = 30),35-44 y 10.1% (n = 79), 45- 54 y 17.4% (n = 190). Infection s wit hout man ifest illness seem to pr edominate. In 1 area the num ber of pos itive persons was significan tly higher than in the other: In Don aur ies near Illertissen 14 (45%) of 31 prob an ds had elevated IgG titer s. This area and the high level region s excepted, no significant differen ces were demon strable amo ngst the 13 region s of Bavaria included in th is investiga tion.
Introduction Since the tick-borne spirochete Borrelia burgdorferi had been shown to be th e cau sative agent of erythema migrans disease (Lyme disease) studies were initiated in 1983 to gain data on the pr evalence of B. burgdorferi infectio ns in upper Bavari a. Early serological investigations showe d that 40 (16.5%) our of 242 forest workers exhibited evidence of B. burgdorferi infections (1). We now pr esent the result s of a more extended study.
Material and Methods Sera were collected fro m 560 prob and s, includ ing 496 forest wo rkers (fw) - (18 females, 478 males), 44 customs officials and 20 employees of a scientific institute frequently wo rking outdoors. A physical exa minatio n of the probands was undertaken at the time of blood sam pling consideri ng aspec ts of occupationa l medicine. Special atte ntio n was given to symptoms possibly related to erythema migrans, meni ngorad iculitis and joint desease. The prob ands were also questioned as to the altitude of their working locati on and the frequency of tick bites. All findings and answers were ente red into a sta nda rdized form .
Borrelia Antibodies in Forest Workers
413
Fig. 1. Map of Bavaria including the 13 regions.
The study took place in 72 forest and customs stations in different areas of Bavaria. In order to secure a statistical comparability the areas were grouped into 13 regions following geographicalphyiscal boundaries (2) as shown in fig. 1. Further data concerning the regions are shown in table
1. Nearly all probands originated from rural areas, generally the places of residence and work were identical. The average age of the fw was 44. 7 y, of the customs officers 36.1 y with a range from 17 to 63 y. This age distributions are shown in fig. 2. The third group of outdoor workers had an average age of 42 .2 y. The majority of fw started working in their profession at the age of 20 y and have comparable curriculum vitae. The age therefore provides a good measure of the length of exposure. The sera were tested for antibodies against B. burgdorferi (13 31 ) by indirect immunofluorescence as described by Wilske et al. (3). IgGantibody titers of i;; 1:64 were regarded as significant-
414
Peter Miinchhoff et al.
Table 1. Number and name of region with: the total number of probands; number of probands with a positive titer of antibodies against B.burgdorferi, percentage; number of forest workers (fw), number and percentage of IgG pos. fw; average age of pos. a. neg. fw; number of customs officers and of the other outdoor workers
Region 1. Nordliche Kalkhochalpen 2. Schwabische u. Oberbayer. Voralpen 3. Voralpines Hugel- u. Moorland 4. Donau Schotterplatte und Unterbayer. Hiigelland 5. Oberpfalzisches und Obermainisches Hiigelland 6. Frankische Alb 7. Nordlinger Ries 8. Fran kisches Keuper Lias Land 9. Mainfrankische Platte 10. Thuringisch -Frankisches Gebirge 11. Hinterer und vorderer Oberpfalzer Wald 12. Hinterer und vorderer Bayerischer Wald 13. Regensenke und Falkensteiner Vorwald not to classify tot al
Total IgG pos. % n
n
forest workers IgG pos. n % n
customs officers age y total
other total
0 0
0 0
40.4 22.3
0 9
0 0
2 23
30 1 65 15
3 23
38.9 40.9
0 0
0 0
7
19
36
7
19
50 .6
0
0
29 5 47 10 77 8 37 3 70 9 28 4
17 21 10 8 13 14
29 5 47 10 77 8 37 3 65 9 16 4
17 21 8 14 25
44.4 0 43.1 0 45.3 0 45.5 0 44.3 5 49.5 12
0 0 0 0 0 0
50.5 18
0
50.5
0
0
0
0
44.7 44
20
11 16
0 0
0 0
50 1 65 15 36
11
7
10
69
4
6
51
3
6
20
3
15
20
3
15
5
0
0
5
0
0
560 69
12.3
496 68
13.7
ly elevated. Sera exhibiting high IgG titers were tested for specific IgG antibodies after preprecipitation with anti-IgG serum. Only one of the 74 control probands (aged 17-60 y in analogy to the age distribution of the fw ) without evidence of tick bites showed an IgG titer of 1:64 (1).
Results The serological results obtained in the 13 regions are summarize d in table 1. It should be noted, that the number of positive probands is significantly lower (chi square-test p = 0.028) in hig h level areas (regions 1 and 12 in figure 1) . An area ex hibiting an exceptionally hig h ra te of infections was Donauries near Illertissen (be long to the region 4), where 14 (45%) out of 31 fw had IgG antibodies specific for B.
burgdorferi.
A total of 69 out of 560 probands had significant IgG tit ers against B. burgdorferi, 1 cus toms official and 68 fw (66 males = 12.4% and 2 females = 11.1 %) respecting 12.3% of all probands. The positive customs officer was aged 44 y and lived in the Bavarian Forest at an altitude be tween 800 and 1200 m .
Borrelia Antibodies in Forest Work ers
4 15
42:..? 40
1.Q..:..l
~
30
,ll.:..9 20
-
16 . 7
,.!1..:...5 10 n
64
hl ~ 31
n
17
n
r
21
190
fw co 35 -44
f w co 25-3 4
fw co 15 ':'24
n
79
1
fw co 45- 5 4
n 2 .2 109 r----,n =
fw co 55 -64
clas s es of age
Fig. 2. Age distribution of the forest workers (fw ) and the customs officers (co).
Fig. 3 sho ws that most of the positive probands had IgG titers between 1:64 and 1:5 12. Only in 6 cases titers of 1:1024 to 1:8000 were o bserved. T he average ag e of the IgG positive per son s is 5 1.9 y, the max imu m pr evalence is 6.9 % (SOy) and 5 .5 % (60y). The IgG nega tive fw exh ibited an ave rage age of 44 y. Fig.4 shows the correla tion of IgG titers co mpa red to ave rage age .
\
32
30
r--
-
25
23
~
20 12
r-
10
6
n
22
1 :64
n
17
1 :128
n
8
1 : 256
n
16
1:5 12
f:l
1 :1024
1.5
1. 5 rTI
1 : 20 48
rr-T
1 : 4096
1 : 8 000
c l asses of tite r s
Fig. 3. Distribution of the positive results within the respective classes of titers. n = 69.
416
Peter Miinchhoff et al. titer
8000
2048
•
.n4
1024
512
•
nl
n 16
256
e n8
128
n17
e
64
n2 1
e
40
I
45
,
,
•
50
55
60
65
age
Fig. 4. Relation between age and titer in the group of the 68 IgG pas. forest workers .
25
23 . 8 r-
20 17. 4
-
15
10 .1
10
.-
5
1. 6
~
15-2 4
26 /10 . 25-3 4
35- 4 4
45 - 54
Fig. 5. Relative frequency of IgG pas . in each age group.
55-6 4
cla sses of a ge
Borrelia Antibodies in Forest Wor kers m
4 17
alt itude 707
7 00
.-612
-
600
5 40 ~
500
n
119 I
n
n
1 59
155
II
III
c las se s of t ick bite fre quency
Fig. 6. Statements about frequency of tick bites in the group of the IgG neg. and pos. (lined) forest work ers (n = 433).
%
3 2. 3 30
26.6
27 . 9
20
10
7.9
11 5 III
c la s se s of tick bi t e frequen cy
Fig. 7. Average of the altitude of the working location related to classes of tick bite frequency. 27
Zbl. Bakt. Hyg. A 263/3
418
Peter Miinchhoff et al.
The frequency of positive probands in different age groups is shown in fig. 5. Starting with age 40 the prevalence increases with a rate of about 0.7% per year. At the time of physical examination no symptoms of erythema migrans disease were encountered. Data concerning previous illness were too unreliable for statistical evaluation. Answers with respect to the frequency of tick bites were classified into 3 groups: 1.) no tick bite during the last 5 years ; 2.) 1-3 bites per year during the last 5 y; 3. ) more than 4 bites a year . In some cases 50 to 100 tick bites per year were reported. Frequent tick bites predominate in the group of serological positive fw whereas in the negative group an almost equal distribution to the 3 categories is found (fig. 6). As shown in fig. 7 the frequency of tick bites decreases with increasing altitude. Most of the investigated work locations are situated at altitudes of 500 to 750 m. 4 probands had specific IgM titers of more than 1:64. None of them showed signs of acute illness.
Discussion The different numbers of seropositive results found in fw and customs officials are not comparable because of a different age distribution. The average age of 44 y and 36.1 y shows a statistically significant difference (p 0.001 t-test). Furthermore the frequency and length of exposure may not be comparable. Limiting all further considerations to the 496 fw the following assumptions can be drawn : The prevelance of IgG positive probands increases with age. Above the age of 40 y the increase seems to be about 0.7% per year (Fig. 5). The average age of the seropositive group (52 y) differs significantly (p 0.001 t-test) from the average age (44y) of the seronegative group. There exists a negative correlation between the IgG titer value and the age (Fig. 4). Fig. 6 indicates a positive correlation between the number of seropositive cases and the frequency of tick bites even though the retrospective inquiry about tick bites may have yielded not altogether reliable results. The tick bite frequency itself depends on the altitude of the working place (Fig. 7) and may be an explanation of our finding, that the frequency of seropositive results decreases with altitude. There are no data available as to whether the B. burgdorferi infection rate of ticks is dependent on altitude. Comparing single forest areas within a given region no significant differences are found with the exception of the Donauries (riverside forests are excellent breeding grounds for ticks) and of the high level regions 1 and 12. It should be pointed outthat not all B. burgdorferi infections in man induce the production of specific antibodies. Even infections with clinical manifestations may remain seronegative. The number of persons exposed to B. burgdorferi infection is certainly appreciably higher than that indicated by serological surveys. Furthermore the incidence of positive results is dependent on technical details . Using another B. burgdorferi strain than B31 may lead to different titers in indirect immunofluorescence. None of the probands had symptoms of infection due to B.burgdorferi at the time of investigation, including persons showing high IgG and/or IgM titers indicating a more recent infection . Further investigations are necessary to assess the clinical importance of serological surveys in B. burgdorferi infections. But there can be no doubt that forest workers have a significantly greater risk on being infected than most other population groups and therefore erythema migrans disease may well be regarded as occuptionaI illness.
Borrelia Antibodies in Forest Workers
419
References 1. Wilske, B., P. Miinchhoff, G. Schierz, V. Preac-Mursic, M. Roggendorf, G. Zoulek: Zur
Epidemiologie der Borrelia burgdorferi Infektion bei Waldarbeitern aus Oberbayern. Munch. Med. Wschr. 127 (1985) 171- 172. 2. Naturraurnliche Gliederung und Waldverbreitung in "Die Bundesrepublik Deutschland in Karren". Herausg.: Statistisches Bundesamt, Institut fur Landeskunde und Raumforschung. 1962 3. Wilske, B., G. Schierz, V. Preac-Mursic, K. Weber, H. W. Pfister, K. Einhaupl: Serological diagnosis of erythema migrans disease and related disorders. Infection, S (1984) 331-33 7.
Peter Miinchhoff, Berufsgenossenschaftlicher Arbeitsmedizinischer Dienst, Zentrum Miinchen, Schwanthaler Str. 111, 8000 Munchen 2, FRG
Antibodies against Borrelia burgdorferi in Bavarian Forest Workers PETER MUNCHHOFF 2 , BETTINA WILSKE 1 , VERA PREA C-MURSIC I , and GUNTER SCHIERZ 1 . I M ax von Pett enkofer-Institut fur Hygiene und Medizinische Mikro biologie der Ludwig Maxirnilians-Universirat Mii nchen, FRG Direktor : Pro f. Dr. F. Deinhardt 2 Beru fsgenossenschaftl icher Arbeitsme dizin ischer Dienst, Zentrum Mii nchen, FRG
Summary The sera of 496 forest workers (fw), 44 custo ms officials and 20 other person s in outdoor profession s from different areas of Bavaria were tested for anti bodies against Borrelia burgdorferi (strain B 31) by indirect immuno fluo rescence. In sera previously abso rbed with Treponema pbagedenis ultr asoni cate, significan tly elevated IgG antibody titers were found in 69 cases, in 68 fw (13,7%) and 1 custom agent . In accor dance with previous observations the distributi on of pos itive results show ed a distin ct age dependan ce: under 24 years (y) 1.6% (n = 64),25-34 y 0 (n = 30),35-44 y 10.1% (n = 79), 45- 54 y 17.4% (n = 190). Infection s wit hout man ifest illness seem to pr edominate. In 1 area the num ber of pos itive persons was significan tly higher than in the other: In Don aur ies near Illertissen 14 (45%) of 31 prob an ds had elevated IgG titer s. This area and the high level region s excepted, no significant differen ces were demon strable amo ngst the 13 region s of Bavaria included in th is investiga tion.
Introduction Since the tick-borne spirochete Borrelia burgdorferi had been shown to be th e cau sative agent of erythema migrans disease (Lyme disease) studies were initiated in 1983 to gain data on the pr evalence of B. burgdorferi infectio ns in upper Bavari a. Early serological investigations showe d that 40 (16.5%) our of 242 forest workers exhibited evidence of B. burgdorferi infections (1). We now pr esent the result s of a more extended study.
Material and Methods Sera were collected fro m 560 prob and s, includ ing 496 forest wo rkers (fw) - (18 females, 478 males), 44 customs officials and 20 employees of a scientific institute frequently wo rking outdoors. A physical exa minatio n of the probands was undertaken at the time of blood sam pling consideri ng aspec ts of occupationa l medicine. Special atte ntio n was given to symptoms possibly related to erythema migrans, meni ngorad iculitis and joint desease. The prob ands were also questioned as to the altitude of their working locati on and the frequency of tick bites. All findings and answers were ente red into a sta nda rdized form .
Borrelia Antibodies in Forest Workers
413
Fig. 1. Map of Bavaria including the 13 regions.
The study took place in 72 forest and customs stations in different areas of Bavaria. In order to secure a statistical comparability the areas were grouped into 13 regions following geographicalphyiscal boundaries (2) as shown in fig. 1. Further data concerning the regions are shown in table
1. Nearly all probands originated from rural areas, generally the places of residence and work were identical. The average age of the fw was 44. 7 y, of the customs officers 36.1 y with a range from 17 to 63 y. This age distributions are shown in fig. 2. The third group of outdoor workers had an average age of 42 .2 y. The majority of fw started working in their profession at the age of 20 y and have comparable curriculum vitae. The age therefore provides a good measure of the length of exposure. The sera were tested for antibodies against B. burgdorferi (13 31 ) by indirect immunofluorescence as described by Wilske et al. (3). IgGantibody titers of i;; 1:64 were regarded as significant-
414
Peter Miinchhoff et al.
Table 1. Number and name of region with: the total number of probands; number of probands with a positive titer of antibodies against B.burgdorferi, percentage; number of forest workers (fw), number and percentage of IgG pos. fw; average age of pos. a. neg. fw; number of customs officers and of the other outdoor workers
Region 1. Nordliche Kalkhochalpen 2. Schwabische u. Oberbayer. Voralpen 3. Voralpines Hugel- u. Moorland 4. Donau Schotterplatte und Unterbayer. Hiigelland 5. Oberpfalzisches und Obermainisches Hiigelland 6. Frankische Alb 7. Nordlinger Ries 8. Fran kisches Keuper Lias Land 9. Mainfrankische Platte 10. Thuringisch -Frankisches Gebirge 11. Hinterer und vorderer Oberpfalzer Wald 12. Hinterer und vorderer Bayerischer Wald 13. Regensenke und Falkensteiner Vorwald not to classify tot al
Total IgG pos. % n
n
forest workers IgG pos. n % n
customs officers age y total
other total
0 0
0 0
40.4 22.3
0 9
0 0
2 23
30 1 65 15
3 23
38.9 40.9
0 0
0 0
7
19
36
7
19
50 .6
0
0
29 5 47 10 77 8 37 3 70 9 28 4
17 21 10 8 13 14
29 5 47 10 77 8 37 3 65 9 16 4
17 21 8 14 25
44.4 0 43.1 0 45.3 0 45.5 0 44.3 5 49.5 12
0 0 0 0 0 0
50.5 18
0
50.5
0
0
0
0
44.7 44
20
11 16
0 0
0 0
50 1 65 15 36
11
7
10
69
4
6
51
3
6
20
3
15
20
3
15
5
0
0
5
0
0
560 69
12.3
496 68
13.7
ly elevated. Sera exhibiting high IgG titers were tested for specific IgG antibodies after preprecipitation with anti-IgG serum. Only one of the 74 control probands (aged 17-60 y in analogy to the age distribution of the fw ) without evidence of tick bites showed an IgG titer of 1:64 (1).
Results The serological results obtained in the 13 regions are summarize d in table 1. It should be noted, that the number of positive probands is significantly lower (chi square-test p = 0.028) in hig h level areas (regions 1 and 12 in figure 1) . An area ex hibiting an exceptionally hig h ra te of infections was Donauries near Illertissen (be long to the region 4), where 14 (45%) out of 31 fw had IgG antibodies specific for B.
burgdorferi.
A total of 69 out of 560 probands had significant IgG tit ers against B. burgdorferi, 1 cus toms official and 68 fw (66 males = 12.4% and 2 females = 11.1 %) respecting 12.3% of all probands. The positive customs officer was aged 44 y and lived in the Bavarian Forest at an altitude be tween 800 and 1200 m .
Borrelia Antibodies in Forest Work ers
4 15
42:..? 40
1.Q..:..l
~
30
,ll.:..9 20
-
16 . 7
,.!1..:...5 10 n
64
hl ~ 31
n
17
n
r
21
190
fw co 35 -44
f w co 25-3 4
fw co 15 ':'24
n
79
1
fw co 45- 5 4
n 2 .2 109 r----,n =
fw co 55 -64
clas s es of age
Fig. 2. Age distribution of the forest workers (fw ) and the customs officers (co).
Fig. 3 sho ws that most of the positive probands had IgG titers between 1:64 and 1:5 12. Only in 6 cases titers of 1:1024 to 1:8000 were o bserved. T he average ag e of the IgG positive per son s is 5 1.9 y, the max imu m pr evalence is 6.9 % (SOy) and 5 .5 % (60y). The IgG nega tive fw exh ibited an ave rage age of 44 y. Fig.4 shows the correla tion of IgG titers co mpa red to ave rage age .
\
32
30
r--
-
25
23
~
20 12
r-
10
6
n
22
1 :64
n
17
1 :128
n
8
1 : 256
n
16
1:5 12
f:l
1 :1024
1.5
1. 5 rTI
1 : 20 48
rr-T
1 : 4096
1 : 8 000
c l asses of tite r s
Fig. 3. Distribution of the positive results within the respective classes of titers. n = 69.
416
Peter Miinchhoff et al. titer
8000
2048
•
.n4
1024
512
•
nl
n 16
256
e n8
128
n17
e
64
n2 1
e
40
I
45
,
,
•
50
55
60
65
age
Fig. 4. Relation between age and titer in the group of the 68 IgG pas. forest workers .
25
23 . 8 r-
20 17. 4
-
15
10 .1
10
.-
5
1. 6
~
15-2 4
26 /10 . 25-3 4
35- 4 4
45 - 54
Fig. 5. Relative frequency of IgG pas . in each age group.
55-6 4
cla sses of a ge
Borrelia Antibodies in Forest Wor kers m
4 17
alt itude 707
7 00
.-612
-
600
5 40 ~
500
n
119 I
n
n
1 59
155
II
III
c las se s of t ick bite fre quency
Fig. 6. Statements about frequency of tick bites in the group of the IgG neg. and pos. (lined) forest work ers (n = 433).
%
3 2. 3 30
26.6
27 . 9
20
10
7.9
11 5 III
c la s se s of tick bi t e frequen cy
Fig. 7. Average of the altitude of the working location related to classes of tick bite frequency. 27
Zbl. Bakt. Hyg. A 263/3
418
Peter Miinchhoff et al.
The frequency of positive probands in different age groups is shown in fig. 5. Starting with age 40 the prevalence increases with a rate of about 0.7% per year. At the time of physical examination no symptoms of erythema migrans disease were encountered. Data concerning previous illness were too unreliable for statistical evaluation. Answers with respect to the frequency of tick bites were classified into 3 groups: 1.) no tick bite during the last 5 years ; 2.) 1-3 bites per year during the last 5 y; 3. ) more than 4 bites a year . In some cases 50 to 100 tick bites per year were reported. Frequent tick bites predominate in the group of serological positive fw whereas in the negative group an almost equal distribution to the 3 categories is found (fig. 6). As shown in fig. 7 the frequency of tick bites decreases with increasing altitude. Most of the investigated work locations are situated at altitudes of 500 to 750 m. 4 probands had specific IgM titers of more than 1:64. None of them showed signs of acute illness.
Discussion The different numbers of seropositive results found in fw and customs officials are not comparable because of a different age distribution. The average age of 44 y and 36.1 y shows a statistically significant difference (p 0.001 t-test). Furthermore the frequency and length of exposure may not be comparable. Limiting all further considerations to the 496 fw the following assumptions can be drawn : The prevelance of IgG positive probands increases with age. Above the age of 40 y the increase seems to be about 0.7% per year (Fig. 5). The average age of the seropositive group (52 y) differs significantly (p 0.001 t-test) from the average age (44y) of the seronegative group. There exists a negative correlation between the IgG titer value and the age (Fig. 4). Fig. 6 indicates a positive correlation between the number of seropositive cases and the frequency of tick bites even though the retrospective inquiry about tick bites may have yielded not altogether reliable results. The tick bite frequency itself depends on the altitude of the working place (Fig. 7) and may be an explanation of our finding, that the frequency of seropositive results decreases with altitude. There are no data available as to whether the B. burgdorferi infection rate of ticks is dependent on altitude. Comparing single forest areas within a given region no significant differences are found with the exception of the Donauries (riverside forests are excellent breeding grounds for ticks) and of the high level regions 1 and 12. It should be pointed outthat not all B. burgdorferi infections in man induce the production of specific antibodies. Even infections with clinical manifestations may remain seronegative. The number of persons exposed to B. burgdorferi infection is certainly appreciably higher than that indicated by serological surveys. Furthermore the incidence of positive results is dependent on technical details . Using another B. burgdorferi strain than B31 may lead to different titers in indirect immunofluorescence. None of the probands had symptoms of infection due to B.burgdorferi at the time of investigation, including persons showing high IgG and/or IgM titers indicating a more recent infection . Further investigations are necessary to assess the clinical importance of serological surveys in B. burgdorferi infections. But there can be no doubt that forest workers have a significantly greater risk on being infected than most other population groups and therefore erythema migrans disease may well be regarded as occuptionaI illness.
Borrelia Antibodies in Forest Workers
419
References 1. Wilske, B., P. Miinchhoff, G. Schierz, V. Preac-Mursic, M. Roggendorf, G. Zoulek: Zur
Epidemiologie der Borrelia burgdorferi Infektion bei Waldarbeitern aus Oberbayern. Munch. Med. Wschr. 127 (1985) 171- 172. 2. Naturraurnliche Gliederung und Waldverbreitung in "Die Bundesrepublik Deutschland in Karren". Herausg.: Statistisches Bundesamt, Institut fur Landeskunde und Raumforschung. 1962 3. Wilske, B., G. Schierz, V. Preac-Mursic, K. Weber, H. W. Pfister, K. Einhaupl: Serological diagnosis of erythema migrans disease and related disorders. Infection, S (1984) 331-33 7.
Peter Miinchhoff, Berufsgenossenschaftlicher Arbeitsmedizinischer Dienst, Zentrum Miinchen, Schwanthaler Str. 111, 8000 Munchen 2, FRG