Epidemiology and Infection



A boarding school outbreak of pertussis in adolescents: value of laboratory diagnostic methods


P. HORBY a1a2, C. R. MACINTYRE a2c1, P. B. McINTYRE a2, G. L. GILBERT a3, M. STAFF a4, M. HANLON a5, L. G. HERON a6, M. CAGNEY a2 and C. BENNETT a4
a1 Communicable Disease Surveillance and Response, World Health Organization, Ha Noi, Viet Nam
a2 National Centre for Immunisation Research and Surveillance of Vaccine Preventable Diseases, The Children's Hospital at Westmead and the University of Sydney, New South Wales, Australia
a3 Centre for Infectious Diseases and Microbiology, Institute of Clinical Pathology and Medical Research, Westmead Hospital, Westmead, New South Wales, Australia
a4 Northern Public Health Unit, NSW Health, Australia
a5 Department of Immunology, Children's Hospital at Westmead, NSW, Australia
a6 South Western Sydney Public Health Unit, NSW Health, Australia

Article author query
horby p   [PubMed][Google Scholar] 
macintyre cr   [PubMed][Google Scholar] 
mcintyre pb   [PubMed][Google Scholar] 
gilbert gl   [PubMed][Google Scholar] 
staff m   [PubMed][Google Scholar] 
hanlon m   [PubMed][Google Scholar] 
heron lg   [PubMed][Google Scholar] 
cagney m   [PubMed][Google Scholar] 
bennett c   [PubMed][Google Scholar] 

Abstract

Culture for Bordetella pertussis (B. pertussis) is the traditional gold standard for laboratory diagnosis of pertussis but is insensitive, especially later in the course of illness and in vaccinated persons. Interpretation of serology is limited by the lack of an appropriate reference standard. An outbreak of pertussis in a crowded boarding-school dormitory allowed evaluation of laboratory correlates of infection. Questionnaires, serum samples and throat swabs were collected from members of the exposed group. Serum samples from unexposed controls of a similar age group were used for comparison. B. pertussis PCR was performed on throat swabs, and sera were tested for IgA antibodies against whole-cell (WC) B. pertussis antigen and IgG antibodies to pertussis toxin (PT). The Centers for Disease Control and Prevention definition for pertussis was used to define clinical cases. We evaluated the use of a previously published cut-off for PT IgG of 125 EIA units (EU)/ml. Completed questionnaires were obtained from 115 students, of whom 85 (74%) reported coughing symptoms, including 32 (28%) who met the clinical case definition for pertussis. B. pertussis was detected by PCR in 17 (15%) and WC IgA in 22 (19%) students; neither correlated with symptoms, but dormitory of residence strongly predicted PCR status. The mean PT IgG geometric mean concentration, in this situation of high pertussis exposure, correlated with severity of symptoms and was significantly higher in both symptomatic and asymptomatic children exposed during the outbreak (P<0·001) than in control children. A cut-off for PT IgG of 125 EU/ml was too high in an outbreak situation to be sensitive enough to identify pertussis cases. A case of pertussis in a crowded boarding-school dormitory resulted rapidly in an outbreak. Serology and PCR were useful in identifying the outbreak and commencing disease control measures. The use of serology has mostly been evaluated in community serosurveys, where it is not possible to determine if immunity reflects vaccination, asymptomatic disease or symptomatic disease. This outbreak gave us the opportunity to evaluate the value of serology and PCR in the presence of confirmed exposure to pertussis.

(Accepted October 23 2004)


Correspondence:
c1 A/Professor C. R. MacIntyre, National Centre for Immunisation Research and Surveillance of Vaccine Preventable Diseases (NCIRS), Locked Bag 4001, Westmead, NSW 2145, Australia. (Email: RainaM@chw.edu.au)


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