Case—control study on encephalopathy associated with diphtheria—tetanus immunization in Campania, Italy

Bulletin ofthe WorldHealth Organization, 63 (5): 919 - 925 (1985) i World Health Organization 1985 Case-control study on encephalopathy associated with diphtheria-tetanus immunization in Campania, Italy D. GRECO' Between 1980 and 1982 in the Campania region of Italy, several cases of encephalo- pathy in children who had only a weekpreviously been given diphtheria-tetanus immuniza- tions were reported to the Italian Ministry of Health in Rome. A case-control study was therefore set up to test the association between the syndrome and immunization. For this purpose, cases were defined as children between 3 and 48 months who had been admitted to an intensive care unit with symptoms such as convulsions of unknown origin, Reye's syndrome, or death from unknown causes. The fatality ratefrom encephalopathy among the immunized children in the study was 25 out of29 (86%o). In Campania (population 5.4 million), the annual incidence of encephalopathy associated with diphtheria-tetanus immunization was estimated to be 2.9 per 100 000 doses of the vaccine. Between January 1980 and February 1983 several reports reached the Italian Ministry of Health about encephalopathic syndromes in children during the week after diphtheria-tetanus immunization, the majority of cases being in the Campania region. Most of these cases were admitted to the paediatric intensive care unit at the Santabono Hospital in Naples, and most proved fatal. Investigations in 1979 and 1980 on similar cases had failed to establish an association with diphtheria-tetanus vaccine. After consultation with WHO, however, a case-control study was initiated to test the association between the observed encephalopathic syndrome and diphtheria- tetanus immunization in the cases reported between 1 January 1980 and 28 February 1983. The results of this investigation are reported below. MATERIALS AND METHODS Case definition For the purpose of this study, a case was defined as a patient aged between 3 and 48 months who had been admitted to the intensive care unit at Santobono Hospital during the study period with one or more of the following diagnoses: coma due to unknown causes, Reye's syndrome, convulsions due to unknown causes, respiratory distress with coma due to unknown causes, death from unknown causes, or X Director, Infectious Diseases Department, Laboratory of Epi- demiology and Biostatistics, and Principal Investigator of the WHO Collaborating Centre for Health and Disease Surveillance, Instituto Superiore di SanitA, Viale Regina Elena 299, 00161 Roma- Nomentano, Rome, Italy. stupor due to unknown causes. Possible cases were identified from the intensive care unit register, and the medical records of the patients were examined in detail before final selection for inclusion in the study. Controls Four controls, two "hospital" controls and two "residence" controls, were obtained for each case. The hospital controls were selected from patients admitted to the Santobono intensive care unit during the study period and were matched to the case by sex, date of admission (± 30 days), and age (± 6 months). Controls younger than 3 months of age were not accepted, i.e., a control for a 4-month-old case would be a child aged from 3 to 10 months. The selected hospital controls had different diagnoses from the cases. The residence controls were chosen from the birth register. These controls were matched to cases by sex, place of residence (by zone for Naples and by town elsewhere), and age (± 1 month), and were alive at the time the cases were admitted to the hospital. Verification of the immunization status of cases and controls Every child born in Italy is compulsorily entered on an immunization register, and an immunization form is held at his or her place of birth, irrespective of the status of immunization. These documents were the data source for the risk factor investigation in the present study. The registers were searched for the immunization records of all cases and controls immunized during 459 -919- D. GRECO the month preceding their admission to the intensive care unit. Details of the type and dose of vaccine received, including its lot number and the name of the factory that had produced it were noted. If no immunization was recorded in the register for the month prior to case hospitalization, the dates of any diphtheria-tetanus or diphtheria-pertussis-tetanus injections received prior to hospitalization were noted. If no immunization records for the individuals in the study were found at their place of birth, a search for change of residence was made, and an exhaustive search of the immunization register of the new place of residence was carried out until evidence of immunization or of refusal was found. Statistical analysis Data were analysed on an ISS IBM 4341 computer using a biomedical statistical package (2). The statistical significance of differences between cases and controls was verified using the Miettinen modification of the Mantel-Haenszel test (4); the odds ratio for unmatched sets was calculated as described by others (3-8). RESULTS The study involved 45 cases that satisfied the above definition; 90 hospital controls matched by age, sex, and date of admission; and 90 residence controls matched by age, sex, and place of residence. Information on risk factors was obtained from all study members. The age and sex of cases are shown in Table 1. Sex matching was biased for one pair of residence controls, and two pairs of hospital controls lay outside the matching range for age. The geographical distribution of cases is shown in Table 1. Age and sex distribution of 45 cases admitted to Santobono Hospital during the study period Males Females Age (months) No. % No. % 3-6 9 35 6 31 7-12 4 15 3 16 13-18 6 23 7 37 19-24 4 15 2 10 25-30 2 8 1 5 31-48 1 4 - - Total 26 100 19 100 Fig. 1. Geographical distribution of cases in Campania. Fig. 1. Twelve cases originated from the city of Naples itself, 23 from Naples province, and 10 from else- where. Of the cases, 80% died during or immediately after the hospital stay, but death occurred in only 247o of the hospital controls for whom information was available. The diagnoses for cases and hospital controls are shown in Table 2. The results of the following clinical tests and examinations were available for all cases and hospital controls, other than those dead at admission: Table 2. Diagnoses for cases and hospital controls Hospital Cases controls Diagnosis No. % No. % Reye's syndrome 11 25 - - Coma, origin unknown 10 22 - - Convulsions, origin unknown 9 20 - - Coma and respiratory distress 9 20 - Stupor, origin unknown 4 9 - - Dead on arrival, origin unknown 2 4 - - Ingestion/inhalation of toxins, foreign bodies - - 37 41 Lower respiratory tract infections - - 18 20 Other infections - - 12 13 Meningitis/septicaemia - - 8 9 Burns - - 6 7 Post-surgical complications - - 5 6 Trauma - - 4 4 Total 45 100 90 100 920 ENCEPHALOPATHY ASSOCIATED WITH DIPHTHERIA-TETANUS IMMUNIZATION Table 3. Immunization history of cases and controls Hospital Residence Immunization with Cases controls controls diphtheria-tetanus toxoid No. % No. % No. % Immunized within previous month 29 64 9 10 12 13 Not immunized within previous month 8 18 48 53 68 76 Never immunized 8 18 33 37 10 11 Total 45 100 90 100 90 100 blood ammonia level, cerebrospinal fluid examin- ation, hepatic enzyme levels, electroencephalogram, electrocardiogram, and X-ray examination; however, for hospital controls with burns or trauma or who had ingested foreign substances, examination of cerebro- spinal fluid was not routinely performed. In addition, autopsies were performed on all hospital deaths. Table 3 shows the immunization history of cases and controls: 29 (647o) of the cases had received a diphtheria-tetanus toxoid injection during the month prior to hospital admission, but only 10% of the hospital controls and 13/o of the residence controls were similarly immunized. No child received diphtheria-pertussis-tetanus vaccine, since this is not routinely given by the public health services in Italy. The results of the case-control analysis of immunization with diphtheria-tetanus toxoid are shown in Table 4. Cases and controls were compared as follows: (1) 45 sets of 1 case and 4 controls immunized during the previous month or previous week; (2) 45 sets of 1 case and 2 hospital controls immunized in the previous month; and (3) 45 sets of 1 case and 2 residence controls. All differences between cases and controls are statistically highly significant, as shown by the results of the x2 test and P value; the relative risks with their confidence limits at the 95% level are also shown. Table 5 shows the number of days that elapsed between immunization and hospital admission for Table 4. Immunization status of cases and controls with diphtheria-tetanus toxoid No. of immunized controls for each case No. and composition of sets 0 1 2 3 4 Total x2 P value Relative risksb 45 sets of 1 case and 4 controls:a Cases immunized within previous month 17 7 3 2 0 29 aevosno nie 62.2 1.27x 10-8 40.9 (16.3-102.5)Cas s not Immu zed within previous month 14 2 0 0 0 16 Cases immunized within previous week 22 3 0 0 0 25 Caeno *muie 83.8 1.32x 10-'° 92.6 (35.1-244.1)Cases t Im un zed within previous week 19 1 0 0 0 20 45 sets of 1 case and 2 hospital controls: Cases immunized within previous month 21 7 1 29 Cases not immunized 42.8 4.4x 10-6 291.9 (53.3-1596.9) within previous month 16 0 0 16 45 sets of 1 case and 2 residence controls: Cases immunized within previous month 21 6 2 29 aevosnot nie 36.4 2.29x 105 22.5 (8.2-62.1)Cas s ot immu zed within previous month 14 2 0 16 a The 4 controls comprised 2 hospital controls and 2 residence controls. b Figures in parentheses give the confidence limits at the 95% level. 921 D. GRECO Table 5. Interval between diphtheria-tetanus immunization and hospital admission of cases and hospital controls Days after immunization 1-3 4-7 8-14 15-30 Total Mean/99% confidence limits No. of cases 12 (41)a 13 (45) 2 (7) 2 (7) 29 (100) 4.44/1.8-7.1 No. of hospital controls 2 (20) 1 (10) 3 (30) 4 (40) 10 (100) 14/4.4-23.6 Total 14 14 5 6 39 a Figures in parentheses are percentages. cases and hospital controls. Eighty-six percent of cases were immunized in the week prior to admission. Analysis of the data by Student's t test (P = 0.0001) shows statistically highly significant differences between the average length of time between immunization and hospital admission of cases and controls. The manufacturer of the diphtheria-tetanus vaccine could be identified for only 17 of the 29 immunized cases (59%), 5 of the 9 immunized hospital controls, and 4 of the 12 immunized residence controls. Table 6 gives the distribution of manufacturers in the three study groups. The distribution of immunized cases as a function of the date of hospital admission is shown in Fig. 2. Twenty-five (86%) of the immunized cases died in hospital. Table 7 gives the dose distribution of diphtheria- tetanus vaccine for the 29 immunized cases. Fifty-one percent of the cases and 28% of the controls received oral polio immunization at the same time as the diphtheria-tetanus injection. Only 13 out of the 29 immunized cases in the study were reported to the health authority as immunization-associated encephalopathy, and the remaining 16 were identified in the course of the study. Of the 23 cases reported to the health authority from January 1980 to December 1982, 10 were not included in this study because they were not admitted to Santobono Hospital (7 cases) or because their diagnosis did not meet the study case definition (3 cases). Is3 2 I JF AU J JASON TDJ F AUJJA SOU ISM iUl J FVAUJ J ASS0 0 IVZ I me Fig. 2. Number of cases per month in Campania over the study period. Table 6. Distribution of manufacturers of diphtheria-tetanus vaccines given to cases and controls during the month before admission of cases to hospital Manufacturer Manufacturer A B C D Known Unknown No. of cases 6 (35)0 4 (24) 5 (29) 2 (12) 17 (59) 12 (41) No. of controls 4 (44) 0 3 (30) 2 (26) 9 (43) 12 (57) Total 10 (38) 4 (15) 8 (30) 4 (15) 26 (52) 24 (48) 0 Figures in parentheses are percentages. 5. , , _ D . 922 I .. 0 1.. I I E.| ENCEPHALOPATHY ASSOCIATED WITH DIPHTHERIA-TETANUS IMMUNIZATION Table 7. Distribution of up to four diphtheria-tetanus vaccine doses in cases and controls immunized within 30 days of hospital admissiona 1st Dose 2nd Dose 3rd Dose 4th Dose Total Cases 11 (38)b 13 (45) 4 (13) 1 (4) 29 (100) Controls 5(24) 15(71) 1 (5) 0 21 (100) a Results not statistically significant. (X2= 4.015; P=0.26). b Figures in parentheses are percentages. Incidence estimation For the study period 1980-83, data on the diphtheria-tetanus doses administered were obtained only for the city of Naples (population 1.3 million). Over this period the total number of doses was 239 802. Twelve cases of encephalopathy occurred in the city over this period, giving an annual incidence rate of 1.6 per 100 000 doses of diphtheria-tetanus vaccine. There is no statistically significant difference between the birth rates in Naples and the Campania region as a whole (population 5.4 million); hence with the assumption that immunization coverage in Campania was the same as that in Naples, we can estimate that 332 000 doses of the vaccine were administered each year in the Campania region as a whole. In the three-year period, 29 cases occurred in Campania in immunized children, giving a mean of 9.6 cases/year, i.e., the annual incidence rate in Campania was 9.6 cases per 332 000 doses or 2.9 cases of encephalopathy per 100 000 doses of diphtheria- tetanus vaccine. DISCUSSION Adverse reactions to immunization have been closely studied in recent years. Most of these studies have been concerned with the diphtheria-pertussis- tetanus vaccine, whereas only a few studies have been concerned with adverse reactions associated with the diphtheria-tetanus vaccine alone (9). In the 1950s (9, 10) and 1960s (11, 12) several studies, mainly in the United Kingdom and the USA, reported different incidences of severe neurological disorders in children who had been immunized with diphtheria-pertussis-tetanus vaccines; incidence rates varied from 1 per 50 000 doses of vaccine (9) to 1 per 10 000 doses (12). The 36 cases of acute neurological illness described in 1974 in the United Kingdom (13) initiated a long debate on the use of diphtheria-pertussis-tetanus vaccines. However, most of these studies were descriptive, lacking control groups, and it was concluded that the illness described represented the normal incidence of such disorders in the population (14). More recently longitudinal studies as well as case-control studies have been undertaken. For example, in the United Kingdom no major neuro- logical damage in immunized children (15) was found after an extensive follow-up investigation. In contrast, the United Kingdom national childhood encephalopathy study (16) revealed a significant association between diphtheria-pertussis-tetanus immunization and severe neurological disorders (1 per 110 000 injections; 95% confidence levels, 1 in 44 000 to 1 in 360 000), but no such association was found when only the small group of persons given diphtheria vaccine was considered. In Italy, only diphtheria-tetanus immunization is compulsory and available free of charge, so that a very small proportion of the population is immunized using diphtheria-pertussis-tetanus vaccine. The present study, dealing only with diphtheria-tetanus immunization, reveals an incidence of 1 case of encephalopathy per 34 500 injections of the vaccine. The results described here indicate a strong association between the incidence of encephalopathy and diphtheria-tetanus immunization in the children admitted to the intensive care unit of Santobono Hospital, with a very high relative risk: thus, a child with encephalopathy was 80 times more likely to have been vaccinated in the previous month than any of the matched controls. From these results, however, it is not possible to infer a causal relationship between immunization and encephalopathy. In addition, because the study was limited to the Campania region, no conclusions can be drawn about the national distribution of complications arising from diphtheria-tetanus immunization, and further studies are needed for this. Detailed clinical observations were not included in this study, other than those needed for case definition. However, the clinical records reviewed indicate the presence of elevated levels of trans- aminases and hyperammoniaemia. The absence of pathological changes in the spinal fluid in many of the cases suggest that most of them had a Reye's-like syndrome. This conclusion is reinforced by the similar incidence rate of cases in our study (about 0.5 per 10 000 children) with that of Reye's syndrome in the USA, although the age groups were different (17). 923 924 D. GRECO ACKNOWLEDGEMENTS The author is indebted to Dr F. Rosmini and Dr S. Salmaso of the Istituto Superiore di Sanita, Rome, for their assistance in the work reported here, as well as to Dr L. Carbone and Dr A. Mele, Health Officials in Naples, and Dr P. Nocerino, Dr F. Zamparelli and Dr Ruggiero of the Santobono Hospital, Naples. The author is also very gateful to Dr B. Lauer, WHO Consultant, for his help in designing the study, and to Mrs S. Luzi, Ms M. E. Sansonetti and Mr C. Curiano for their help in preparing the draft manuscript. RtSUME ETUDE DE CAS-TEMOINS CONDUITE EN CAMPANIE (ITALIE) SUR L'ENCEPHALOPATHIE ASSOCItE A LA VACCINATION CONTRE LA DIPHTERIE ET LE TETANOS Entre janvier 1980 et decembre 1982, on a requ de Campanie un nombre alarmant de rapports faisant etat de cas d'encephalopathie chez des enfants qui avaient et vaccines contre la diphterie et le tetanos dans le courant de la semaine precedente. Une etude de cas-temoins a e entreprise pour elucider une eventuelle correlation entre l'encephalopathie et la vaccination. A cette fin, on a defini comme cas d'encephalopathie un enfant admis a I'unite regionale de soins intensifs de pediatrie (la seule de la region) avec un diagnostic de coma, de syndrome de Reye, de convulsions ou de stupeur-soit au total 45 cas. Pour chacun d'eux, deux temoins apparies pour le sexe, la date d'admission et l'age ont et choisis parmi les sujets admis dans la meme unite et deux temoins apparies pour le sexe, I'age et le lieu de residence ont egalement e selectionnes dans le registre des naissances. Les releves de vaccination ont e examines pour les cas et pour les temoins. Parmi les cas, 29 avaient et vaccines contre la diphterie et le tetanos dans le courant du mois ayant precede l'appa- rition de la maladie, 25 d'entre eux ayant ete vaccines dans le courant de la semaine precedente. En revanche, seuls 21 des temoins hospitaliers et 4 des temoins choisis dans le meme lieu de residence avaient et vaccines. Ces differences sont statistiquement significatives. Parmi les cas vaccines, 380%o avaient requ la premiere dose de vaccin antidiphterique-antitetanique et 45% avaient egalement requ la deuxieme dose; les 17%o restants avaient requ au moins trois doses. Sur les 29 cas vaccines, 25 (86%7o) sont dec6des i l'h8pital. Geographiquement, les cas se repartissaient dans toute la Campanie: 12 etaient de Naples (1,3 millions d'habitants) qui est la capitale de la region. Des donnees sur le nombre de doses de vaccin administr&es par mois n'ont pu etre fournies que pour Naples (239 802 doses au cours des trois ann&es de l'etude). En supposant que la proportion d'enfants vaccines soit la meme a Naples et dans le reste de la Campanie, on peut estimer a 332 000 par an le nombre de doses de vaccin anti- diphterique-antitetanique administrees dans la region (5,4 millions d'habitants), soit 996 000 doses pour les trois annees de l'etude. 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