809
Public Health MATERNAL AND INFANT ANTIBODY RESPONSE TO MENINGOCOCCAL VACCINATION IN PREGNANCY AZARIAS DE ANDRADE CARVALHO CARMEN MARIA S. GIAMPAGLIA HARUE KIMURA OCTAVIO AUGUSTO DE C. PEREIRA CALIL KAIRALLA FARHAT JOSÉ CARLOS NEVES RENATO PRANDINI EDUARDO DA SILVA CARVALHO ANTONIO MIGUEL ZARVOS
Departments of Pœdiatrics and Microbiology and Parasitology, Escola Pavlista de Medicina São Paulo, Brazil The antigenic capacity of a mixed vaccine prepared with polysaccharides of meningococcus groups A and C, the placental transfer of antibodies, and the persistence of positive titres in the infant were evaluated in 21 pregnant women and their offspring during an epidemic of meningitis in São Paulo, Brazil; and antibody response was assessed in 29 infants vaccinated at less than 6 months of age. Antibodies were detected by passive hæmagglutination; the high titres found and the high frequency of positive results are thought to be due to the use of a more sensitive technique. Increased antibody titres were found in most women, and there was evidence for passive transfer to the newborn, especially with regard to antibody type C. However, passive transfer was irregular, and the presence of antibodies in the mother did not guarantee their presence in the child. Passive transfer lasted for only 2-5 months. Vaccination in children under 6 months of age had poor results; only 1 child seroconverted.
Summary
INTRODUCTION
of evidence points to a correlation between meningococcal infection and the absence of humoral1 antibodies: the occurrence of the disease in childhood (except in closed populations3-s), the cyclical rhythm,2.6 the high levels of antibodies found in convalescents,7-9 and the lasting immunity4.1O all favour this correlation. Goldschneider et al. 11 tried to explain the low incidence of clinical meningococcal infection, even in epidemic conditions, in terms of the percentage of the population who lacked detectable antibodies by the possibility of insufficient contact with sources of infection, the involvement of non-humoral defence mechanisms, or the possibility of subclinical infection. They concluded that circulating antibodies in high titre guarantee protection, provided complement levels are sufficient. During a mass vaccination of the population of Sao Paulo with a mixed antimeningococcal vaccine (groups A and C), excepting children under 6 months, we measured the antibody response of pregnant vaccinees, the antibody levels transferred to the child, and the period these antibodies persisted in the child. These data are important because infants only a few months old are frequent victims of the disease, and mortality is high. At a meeting organised by the Pan American Health OrganiA
LOT
sation in February, 1976, in Brasilia, Dr Edmundo Juarez showed that in 1974, during the epidemic in Sao Paulo, the attack frequencies in infants were 4-4%, 9-2%, and 7.5% for groups A and C and for an undetermined group, respectively, the total numbers of patients in that year being 3888, 931, and 7204. Dr Ayrosa Galvao showed that the mortality-rate was 21% for infants and 7 1 % for all people who had the disease in 1974. Another unknown factor is the response to vaccination in children less than 6 months of age. We investigated these children at the same time. MATERIALS AND METHODS
Vaccinees We studied pregnant women seen in the antenatal clinics of the Escola Paulista de Medicina and of the Centro de Atendimento Materno-Infantil do Parque Pirajussara, in the municipality of Embu. Although the programme was explained to the patients when the first blood-sample was taken, a few days before planned vaccination, many women refused the vaccine, fearing that it might damage the fetus; others left the programme subsequently. Women from Vila Pirajussara, an area of poor education, left the programme as soon as they knew that blood-samples would be taken from their children. There was no time for thorough preparation before the mass vaccination started. For the 91 women included in this study, we obtained incomplete samples in 65 and complete information in 21; some cases were lost because the babies were born at home or in distant hospitals or because they did not survive.
Blood-samples (8-10 ml) were centrifuged and kept aseptically in the freezer until the end of the fieldwork. The sera were then sent to the department of microbiology for antibody titration. 29 children, less than 6 months of age cinated too and studied by us.
were vac-
Vaccines
Polysaccharide vaccines of groups A and C duced in the Instituto Butantan, Sao Paulo.
were
used, pro-
Sera
Sera from 21 pregnant women and, subsequently, from their babies were studied. The women, in different periods of pregnancy (2-9 months), were vaccinated on April 24, 1975. 1 of them referred to vaccination about 5 months before. A blood-sample was collected before vaccination, and four or more samples were taken afterwards, covering a period of at least 8 months. Cord blood was sampled, and three or more blood-samples were taken from infants over a period of about 6 months. 29 children, 49-197 days old, were vaccinated, and blood was taken on the day of vaccination and 30, 90, and 180 days afterwards. With only 2 exceptions, the children’s mothers had been vaccinated a year previously. Standard Antimeningococcal Sera We used
antimeningococcal agglutinating
sera
(A
and
C)
produced at the Instituto Adolfo Lutz, Sao Paulo. Sensitisation The
of Erythrocytes
A and C were susconcentration of 1 mg/ml and stored at -20°C. The antigen, diluted in physiological saline solution with 20 mmol/1 sodium hydroxide, was incubated for 18-24 h in water bath at 37°C.’ Group-O, Rh-negative red blood-cells were collected in an equal volume of Alsever’s solution and kept at 4°C. Before use, the cells were washed three times in 10 volumes of physiological saline solution with centrifugation for 10 min. The final deposit was resuspended at 10% in physiological saline solution. Equal volumes of the 10% suspension of erythrocytes and the saline solution of the antigen were mixed and incubated in water bath at 37°C for 2 h, with
pended
lyophilised polysaccharide antigens in saline solution
at a
810 30 min. To control the reaction we used a mixof the 10% suspension of erythrocytes and saline with 20 mmol/1 sodium hydroxide treated as above. After the incubation period the cells were washed three times in 10 volumes of saline to remove excess antigen, and the erythrocytes were suspended in physiological saline solution at 1 %.
shaking every ture
RELATION BETWEEN TITRE OF MATERNAL ANTIBODIES FOR N.MENINGITIDIS A AND C AND THEIR PLACENTAL TRANSFER
Sensitising Concentration of Antigen The ideal sensitising dose was determined by block titration, varying the concentrations of the antigen and of the standard antimeningococcal sera. Sensitisation was best at 50 }jLg/ml for antigen A (corresponding to a dilution 1/20 of the stock solution at 1 mg/ml). For antigen C the best concentration was 11 p.glml (corresponding to a dilution 1/90 of the stock solu-
tion at 1
mg/ml). I
Passive Haemagglutination antibodies of N. meningitidis A the be titrated were inactivated at 56°C for 30 min, and two-fold dilutions were made in saline with 0 - 5 % bovine serum albumin. In tubes, 80 .1 of sensitised erythrocytes was mixed with an equal volume of each dilution of serum. For control, non-sensitised erythrocytes were added to the smallest dilution of each serum. After incubation in a water bath at 370C for 5 min and quick centrifugation, agglutination was verified with a slight agitation of the tube. For C antibodies the procedure was much the same, the reaction taking place in microtitre plates. For
anti-polysaccharide
sera to
RESULTS
Of the 21 pregnant women, only 1 had no detectable antibodies to Neisseria meningitidis group A before vaccination, while 9 were negative for polysaccharide group C. These 9 seroconverted after simultaneous vaccination with polysaccharides A and C, but the group-A-negative woman did not. A 4-fold or greater increase in antibody titre was observed in 9 of the 12 women who had had some anti-C antibody before vaccination and in 15 of the 20 who had been positive for group A (see figure).
I
I
I
I
I
"High transfer" when titre 1/4 of maternal titre is transferred; "Low transfer" when < 1/4 of the mother’s titre is transferred. 1 pregnant woman did not respond to vaccination.
Placental transfer of antibodies was detected in 7 and 14 infants for polysaccharides A and C, respectively, and this passive immunity lasted for 2-5 months. The distribution of the cases in which placental transfer was observed and those in which it was not, according to maternal titre at the moment of delivery is shown in the table. Maternal antibody titres were monitored through at least five serum samples and for a period of 8 months or more. The peak titre was always reached by 30 days after vaccination; it usually stayed at this level or fell by no more than one dilution throughout the period of observation. In 8 cases, 4 for each type of antibody, the titre to values 4-fold (or greater) less than the peak titre, but no positive case became negative. Standard hyperimmune sera, routinely included, were always negative for the heterologous antigen and varied by only one dilution for the homologous one. Among the 29 children given vaccine antibodies were found in the first sample (placental transfer) in 2 children for polysaccharide and in 3 children for polysaccharide C; and 3 children had both. All but 1 of these positives were in children aged less than 3 months at vaccination. There was only 1 seroconversion, against polysaccharide C in the child vaccinated at 197 days of -
age. DISCUSSION
titres against meningococcal polysaccharides A and C before and 30 days after vaccination.
Antibody
The finding of 20 positive sera for polysaccharide A and 12 for polysaccharide C in the 21 sera studied before vaccination might be expected in view of the epidemic of meningitis present at the beginning of this study. We believe that the much higher frequency of positive results in our material compared with that of Takeda et a1.I3 was due to the use of a more sensitive reaction. Maternal antibodies reached high titres and these remained high during the 7-8 months during which we followed up the patients. During this period the titre seldom fell by more than one dilution. Thus, we cannot confirm the short-lived protection that Takeda et al. reported. It is not likely that later contact with meningococci was responsible for maintaining these high titres; the epidemic waned after mass vaccination of the population. Placental transfer of antibodies was irregular, and it
811 clear that the existence of maternal antibodies does not guarantee protection of the newborn and that the chance of transfer is related neither to maternal titre (see table) nor to the period in the pregnancy when the mother was vaccinated (not shown). Vaccination of children in the first 6 months of life was unsuccessful-only 1 seroconversion in 58 (2x29). Residual antibodies resulting from placental transfer were found frequently until 80 days after birth, but rarely after this time. seems
Requests for reprints should be addressed to A. de A. C., Escola Paulista de Medicina, Rua Botucatu, 720,04023-Sao Paulo, Brazil. REFERENCES 1. Horwitz, A., Peroni, J. Archs intern. Med. 1941, 74, 365. 2. Morbid. Mortal. Rep. (annual supplements 1960-66). U.S. Government
Printing Office. 3. Cook, S. S. Am. J. Hyg. 1936, 23, 172. 4. Maxcy, K. F. Preventive Medicine and Public Health; p. 121. New York, 1956. 5 Sartwell, P. E., Smith, W. M. Am. J. publ. Hlth not Hlth. 1944, 34, 40. 6. Morbid. Mortal. wkly Rep. (annual supplement 1966). U.S. Government Printing Office. 7. Houston, T., Rankin, J. C. Br. med. Bull. 1907, 2, 1414. 8. Kabat, E. A., Miller, C. P., Kaiser, H., Foster, A. Z. J. exp. Med. 1945, 81, 1. 9. Thomas, L., Smith, H. W., Dingle, J. H. J. clin. Invest. 1943, 22, 361. 10. Bradford, W. L. in Textbook of Pediatrics (edited by W. E. Nelson); p. 425. Philadelphia, 1959. 11. Goldschneider, I., Gotschlich, E. C., Artenstein, M. S. J. exp. Med. 1969, 129, 1307. 12. Landy, M., Trapani, R. J., Clark, W. R. Am. J. Hyg. 1955, 62, 54. 13. Takeda, A. K., Taunay, A. E., Scalabrini, L. G. P., Castro, I. O. Revta Inst. Adolfo Lutz, 1974, 34, 127.
The design of a controlled trial to test the hypothesis that the condom protects the user against s.T.D. is easy enough, but practical difficulties diminish the feasibility of such a trial. The prospective investigation described here was designed to test the null hypothesis that invariable and correct use of the condom during sexual intercourse would make no difference to the prevalence of gonorrhoea in a group of such users compared with its prevalence in a group of non-users. The population from which the two groups are drawn is a selected onemales attending a large metropolitan clinic specialising in the diagnosis and treatment of sexually transmitted diseases and any conclusions that may be drawn from the results should take this fact into account. PATIENTS AND METHODS
Male patients attending the department of genito-urinary medicine at St Thomas’ Hospital between lst January and 31st July, 1975, were questioned before examination about their contraceptive practice. In particular, they were asked whether they had used a condom with their recent sexual partners and, whether it had been used correctly. "Correctly" meant that the condom had been used throughout each act of sexual intercourse and that there had been no unprotected genital contact before or after intercourse. There were thus 3 groups of patients-correct users, incorrect users, and nonusers.
For the purposes of the null hypothesis, it was assumed that the groups of condom users formed representative sub-groups of the population attending the clinic. Differences between the various diagnoses in the different groups were assessed by the X2 test. RESULTS
THE CONDOM AND GONORRHŒA DAVID BARLOW
Department of Genito-urinary Medicine, St Thomas’ Hospital, London SE1 7EH
of the condom by male patients attending a clinic specialising in sexually transmitted diseases has been assessed over a period of six months. Condom users were divided into those who used them properly and invariably, and those who did not. In the group studied, correct use of the condom was associated with a significantly lower probability of acquiring gonorrhœa (p
Public Health MATERNAL AND INFANT ANTIBODY RESPONSE TO MENINGOCOCCAL VACCINATION IN PREGNANCY AZARIAS DE ANDRADE CARVALHO CARMEN MARIA S. GIAMPAGLIA HARUE KIMURA OCTAVIO AUGUSTO DE C. PEREIRA CALIL KAIRALLA FARHAT JOSÉ CARLOS NEVES RENATO PRANDINI EDUARDO DA SILVA CARVALHO ANTONIO MIGUEL ZARVOS
Departments of Pœdiatrics and Microbiology and Parasitology, Escola Pavlista de Medicina São Paulo, Brazil The antigenic capacity of a mixed vaccine prepared with polysaccharides of meningococcus groups A and C, the placental transfer of antibodies, and the persistence of positive titres in the infant were evaluated in 21 pregnant women and their offspring during an epidemic of meningitis in São Paulo, Brazil; and antibody response was assessed in 29 infants vaccinated at less than 6 months of age. Antibodies were detected by passive hæmagglutination; the high titres found and the high frequency of positive results are thought to be due to the use of a more sensitive technique. Increased antibody titres were found in most women, and there was evidence for passive transfer to the newborn, especially with regard to antibody type C. However, passive transfer was irregular, and the presence of antibodies in the mother did not guarantee their presence in the child. Passive transfer lasted for only 2-5 months. Vaccination in children under 6 months of age had poor results; only 1 child seroconverted.
Summary
INTRODUCTION
of evidence points to a correlation between meningococcal infection and the absence of humoral1 antibodies: the occurrence of the disease in childhood (except in closed populations3-s), the cyclical rhythm,2.6 the high levels of antibodies found in convalescents,7-9 and the lasting immunity4.1O all favour this correlation. Goldschneider et al. 11 tried to explain the low incidence of clinical meningococcal infection, even in epidemic conditions, in terms of the percentage of the population who lacked detectable antibodies by the possibility of insufficient contact with sources of infection, the involvement of non-humoral defence mechanisms, or the possibility of subclinical infection. They concluded that circulating antibodies in high titre guarantee protection, provided complement levels are sufficient. During a mass vaccination of the population of Sao Paulo with a mixed antimeningococcal vaccine (groups A and C), excepting children under 6 months, we measured the antibody response of pregnant vaccinees, the antibody levels transferred to the child, and the period these antibodies persisted in the child. These data are important because infants only a few months old are frequent victims of the disease, and mortality is high. At a meeting organised by the Pan American Health OrganiA
LOT
sation in February, 1976, in Brasilia, Dr Edmundo Juarez showed that in 1974, during the epidemic in Sao Paulo, the attack frequencies in infants were 4-4%, 9-2%, and 7.5% for groups A and C and for an undetermined group, respectively, the total numbers of patients in that year being 3888, 931, and 7204. Dr Ayrosa Galvao showed that the mortality-rate was 21% for infants and 7 1 % for all people who had the disease in 1974. Another unknown factor is the response to vaccination in children less than 6 months of age. We investigated these children at the same time. MATERIALS AND METHODS
Vaccinees We studied pregnant women seen in the antenatal clinics of the Escola Paulista de Medicina and of the Centro de Atendimento Materno-Infantil do Parque Pirajussara, in the municipality of Embu. Although the programme was explained to the patients when the first blood-sample was taken, a few days before planned vaccination, many women refused the vaccine, fearing that it might damage the fetus; others left the programme subsequently. Women from Vila Pirajussara, an area of poor education, left the programme as soon as they knew that blood-samples would be taken from their children. There was no time for thorough preparation before the mass vaccination started. For the 91 women included in this study, we obtained incomplete samples in 65 and complete information in 21; some cases were lost because the babies were born at home or in distant hospitals or because they did not survive.
Blood-samples (8-10 ml) were centrifuged and kept aseptically in the freezer until the end of the fieldwork. The sera were then sent to the department of microbiology for antibody titration. 29 children, less than 6 months of age cinated too and studied by us.
were vac-
Vaccines
Polysaccharide vaccines of groups A and C duced in the Instituto Butantan, Sao Paulo.
were
used, pro-
Sera
Sera from 21 pregnant women and, subsequently, from their babies were studied. The women, in different periods of pregnancy (2-9 months), were vaccinated on April 24, 1975. 1 of them referred to vaccination about 5 months before. A blood-sample was collected before vaccination, and four or more samples were taken afterwards, covering a period of at least 8 months. Cord blood was sampled, and three or more blood-samples were taken from infants over a period of about 6 months. 29 children, 49-197 days old, were vaccinated, and blood was taken on the day of vaccination and 30, 90, and 180 days afterwards. With only 2 exceptions, the children’s mothers had been vaccinated a year previously. Standard Antimeningococcal Sera We used
antimeningococcal agglutinating
sera
(A
and
C)
produced at the Instituto Adolfo Lutz, Sao Paulo. Sensitisation The
of Erythrocytes
A and C were susconcentration of 1 mg/ml and stored at -20°C. The antigen, diluted in physiological saline solution with 20 mmol/1 sodium hydroxide, was incubated for 18-24 h in water bath at 37°C.’ Group-O, Rh-negative red blood-cells were collected in an equal volume of Alsever’s solution and kept at 4°C. Before use, the cells were washed three times in 10 volumes of physiological saline solution with centrifugation for 10 min. The final deposit was resuspended at 10% in physiological saline solution. Equal volumes of the 10% suspension of erythrocytes and the saline solution of the antigen were mixed and incubated in water bath at 37°C for 2 h, with
pended
lyophilised polysaccharide antigens in saline solution
at a
810 30 min. To control the reaction we used a mixof the 10% suspension of erythrocytes and saline with 20 mmol/1 sodium hydroxide treated as above. After the incubation period the cells were washed three times in 10 volumes of saline to remove excess antigen, and the erythrocytes were suspended in physiological saline solution at 1 %.
shaking every ture
RELATION BETWEEN TITRE OF MATERNAL ANTIBODIES FOR N.MENINGITIDIS A AND C AND THEIR PLACENTAL TRANSFER
Sensitising Concentration of Antigen The ideal sensitising dose was determined by block titration, varying the concentrations of the antigen and of the standard antimeningococcal sera. Sensitisation was best at 50 }jLg/ml for antigen A (corresponding to a dilution 1/20 of the stock solution at 1 mg/ml). For antigen C the best concentration was 11 p.glml (corresponding to a dilution 1/90 of the stock solu-
tion at 1
mg/ml). I
Passive Haemagglutination antibodies of N. meningitidis A the be titrated were inactivated at 56°C for 30 min, and two-fold dilutions were made in saline with 0 - 5 % bovine serum albumin. In tubes, 80 .1 of sensitised erythrocytes was mixed with an equal volume of each dilution of serum. For control, non-sensitised erythrocytes were added to the smallest dilution of each serum. After incubation in a water bath at 370C for 5 min and quick centrifugation, agglutination was verified with a slight agitation of the tube. For C antibodies the procedure was much the same, the reaction taking place in microtitre plates. For
anti-polysaccharide
sera to
RESULTS
Of the 21 pregnant women, only 1 had no detectable antibodies to Neisseria meningitidis group A before vaccination, while 9 were negative for polysaccharide group C. These 9 seroconverted after simultaneous vaccination with polysaccharides A and C, but the group-A-negative woman did not. A 4-fold or greater increase in antibody titre was observed in 9 of the 12 women who had had some anti-C antibody before vaccination and in 15 of the 20 who had been positive for group A (see figure).
I
I
I
I
I
"High transfer" when titre 1/4 of maternal titre is transferred; "Low transfer" when < 1/4 of the mother’s titre is transferred. 1 pregnant woman did not respond to vaccination.
Placental transfer of antibodies was detected in 7 and 14 infants for polysaccharides A and C, respectively, and this passive immunity lasted for 2-5 months. The distribution of the cases in which placental transfer was observed and those in which it was not, according to maternal titre at the moment of delivery is shown in the table. Maternal antibody titres were monitored through at least five serum samples and for a period of 8 months or more. The peak titre was always reached by 30 days after vaccination; it usually stayed at this level or fell by no more than one dilution throughout the period of observation. In 8 cases, 4 for each type of antibody, the titre to values 4-fold (or greater) less than the peak titre, but no positive case became negative. Standard hyperimmune sera, routinely included, were always negative for the heterologous antigen and varied by only one dilution for the homologous one. Among the 29 children given vaccine antibodies were found in the first sample (placental transfer) in 2 children for polysaccharide and in 3 children for polysaccharide C; and 3 children had both. All but 1 of these positives were in children aged less than 3 months at vaccination. There was only 1 seroconversion, against polysaccharide C in the child vaccinated at 197 days of -
age. DISCUSSION
titres against meningococcal polysaccharides A and C before and 30 days after vaccination.
Antibody
The finding of 20 positive sera for polysaccharide A and 12 for polysaccharide C in the 21 sera studied before vaccination might be expected in view of the epidemic of meningitis present at the beginning of this study. We believe that the much higher frequency of positive results in our material compared with that of Takeda et a1.I3 was due to the use of a more sensitive reaction. Maternal antibodies reached high titres and these remained high during the 7-8 months during which we followed up the patients. During this period the titre seldom fell by more than one dilution. Thus, we cannot confirm the short-lived protection that Takeda et al. reported. It is not likely that later contact with meningococci was responsible for maintaining these high titres; the epidemic waned after mass vaccination of the population. Placental transfer of antibodies was irregular, and it
811 clear that the existence of maternal antibodies does not guarantee protection of the newborn and that the chance of transfer is related neither to maternal titre (see table) nor to the period in the pregnancy when the mother was vaccinated (not shown). Vaccination of children in the first 6 months of life was unsuccessful-only 1 seroconversion in 58 (2x29). Residual antibodies resulting from placental transfer were found frequently until 80 days after birth, but rarely after this time. seems
Requests for reprints should be addressed to A. de A. C., Escola Paulista de Medicina, Rua Botucatu, 720,04023-Sao Paulo, Brazil. REFERENCES 1. Horwitz, A., Peroni, J. Archs intern. Med. 1941, 74, 365. 2. Morbid. Mortal. Rep. (annual supplements 1960-66). U.S. Government
Printing Office. 3. Cook, S. S. Am. J. Hyg. 1936, 23, 172. 4. Maxcy, K. F. Preventive Medicine and Public Health; p. 121. New York, 1956. 5 Sartwell, P. E., Smith, W. M. Am. J. publ. Hlth not Hlth. 1944, 34, 40. 6. Morbid. Mortal. wkly Rep. (annual supplement 1966). U.S. Government Printing Office. 7. Houston, T., Rankin, J. C. Br. med. Bull. 1907, 2, 1414. 8. Kabat, E. A., Miller, C. P., Kaiser, H., Foster, A. Z. J. exp. Med. 1945, 81, 1. 9. Thomas, L., Smith, H. W., Dingle, J. H. J. clin. Invest. 1943, 22, 361. 10. Bradford, W. L. in Textbook of Pediatrics (edited by W. E. Nelson); p. 425. Philadelphia, 1959. 11. Goldschneider, I., Gotschlich, E. C., Artenstein, M. S. J. exp. Med. 1969, 129, 1307. 12. Landy, M., Trapani, R. J., Clark, W. R. Am. J. Hyg. 1955, 62, 54. 13. Takeda, A. K., Taunay, A. E., Scalabrini, L. G. P., Castro, I. O. Revta Inst. Adolfo Lutz, 1974, 34, 127.
The design of a controlled trial to test the hypothesis that the condom protects the user against s.T.D. is easy enough, but practical difficulties diminish the feasibility of such a trial. The prospective investigation described here was designed to test the null hypothesis that invariable and correct use of the condom during sexual intercourse would make no difference to the prevalence of gonorrhoea in a group of such users compared with its prevalence in a group of non-users. The population from which the two groups are drawn is a selected onemales attending a large metropolitan clinic specialising in the diagnosis and treatment of sexually transmitted diseases and any conclusions that may be drawn from the results should take this fact into account. PATIENTS AND METHODS
Male patients attending the department of genito-urinary medicine at St Thomas’ Hospital between lst January and 31st July, 1975, were questioned before examination about their contraceptive practice. In particular, they were asked whether they had used a condom with their recent sexual partners and, whether it had been used correctly. "Correctly" meant that the condom had been used throughout each act of sexual intercourse and that there had been no unprotected genital contact before or after intercourse. There were thus 3 groups of patients-correct users, incorrect users, and nonusers.
For the purposes of the null hypothesis, it was assumed that the groups of condom users formed representative sub-groups of the population attending the clinic. Differences between the various diagnoses in the different groups were assessed by the X2 test. RESULTS
THE CONDOM AND GONORRHŒA DAVID BARLOW
Department of Genito-urinary Medicine, St Thomas’ Hospital, London SE1 7EH
of the condom by male patients attending a clinic specialising in sexually transmitted diseases has been assessed over a period of six months. Condom users were divided into those who used them properly and invariably, and those who did not. In the group studied, correct use of the condom was associated with a significantly lower probability of acquiring gonorrhœa (p
