The protective effect of immunisation against diphtheria, pertussis and tetanus (DPT) in relation to sudden infant death syndrome

Epidemiological evidence indicates infants immunised against diphtheria, pe rtussis and tetanus (DPT) are at decreased risk of sudden infant death synd rome (SIDS). Asymptomatic whooping cough and pyrogenic toxins of Staphyloco ccus aureus have been implicated in the aetiology of SIDS. The objectives o f the present study were: (1) to determine if the DPT vaccine induced antib odies cross-reactive with the staphylococcal toxins; (2) to determine if an tibodies to the pertussis toxin (PT) and the staphylococcal toxins were pre sent in the sera of women during late pregnancy; (3) to examine the effects of infant immunisation on levels of antibodies to PT and the staphylococca l toxins; (4) to assess the effects of changes in immunisation schedules in the UK on the incidence and age distribution of SIDS. Enzyme-linked immuno sorbent assays (ELISA) were used to measure binding of rabbit or human Ige to the DPT vaccine, PT, toxic shock syndrome toxin-1 (TSST-1) and staphyloc occal enterotoxins A (SEA), B (SEB) and C (SEC). Neutralisation activity of anti-DPT serum was assessed by a bioassay for induction of nitric oxide fr om human monocytes by the staphylococcal toxins. Anti-DPT serum bound to th e DPT vaccine, PT and each of the staphylococcal toxins. It also reduced th e ability of the four toxins to induce nitric oxide from monocytes. In preg nant women, levels of IgG to PT, SEC and TSST-1 decreased significantly in relation to increasing weeks of gestation while antibodies to SEA and SEE i ncreased. In infants' sera there were significant correlations between leve ls of IgG bound to DPT and IgG bound to PT, TSST-1 and SEC but not SEA or S EB. Antibody levels to the toxins in infants declined with age, sera from i nfants less than or equal to 2 months of age had higher levels of IgG bound to the toxins than those older than 2 months. This pattern was observed fo r infants whose immunisation schedules began at 2 months of age or 3 months of age. The decrease in IgG bound to the toxins was, however, less for tho se immunised at 2 months. The decrease in SIDS deaths after the change in i mmunisation schedules was greatest in the 4-6-month age range. While DPT im munisation might prevent some unexplained infant deaths due to asymptomatic whooping cough, these data indicate that immunisation with DPT also induce s antibodies cross-reactive with pyrogenic staphylococcal toxins implicated in many cases of SIDS. Passive immunisation of infants who have low levels of these antibodies might reduce further the numbers of these infant death s. (C) 1999 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.