Delayed immunisation and risk of pertussis in infants: unmatched case-control study

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Abstract
Pertussis remains a severe disease in infants. As about two thirds of infants with pertussis are admitted to hospital, factors that seem to be associated with an increased risk of pertussis may in fact be associated with an increased risk of hospital admission. 1 2 The admission rate for pertussis in New Zealand is five to 10 times higher than in England and Wales and the United States.3 We determined whether immunisation reduced the risk of admission to hospital for pertussis by comparing infants admitted with pertussis and infants admitted with other acute respiratory illnesses. View this table: Odds ratios (95% confidence intervals) of catching pertussis associated with delays in giving pertussis vaccine We performed an unmatched case-control study during the 1995-7 pertussis epidemic in Auckland, New Zealand. Pertussis was defined as cough lasting at least two weeks, with coughing paroxysms, inspiratory “whoop,” or vomiting after coughing. The control group consisted of 98 infants admitted to hospital with a coughing illness who were …