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Question 3 Is measurement of the lymphocyte count useful in the investigation of suspected pertussis in infants?
  1. Ilana Levene,
  2. Ian Wacogne
  1. Correspondence to Ilana Levene, Department of General Paediatrics, Birmingham Children's Hospital, Steelhouse Lane, Birmingham B4 6NH, UK; ilana.levene{at}

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A 3-week-old baby presents with cough and episodes of apnoea. Nasopharyngeal aspirate is negative for common respiratory viruses. You consider the diagnosis of pertussis and take a full blood count to assess the lymphocyte count. You wonder what the sensitivity and specificity of the lymphocyte count is for pertussis in infants.

Structured clinical question

In an infant with clinical suspicion of pertussis [patient], how useful is a lymphocyte count [intervention] to determine the likelihood of a positive or negative diagnosis [outcome]?

Search strategy

Secondary sources

A search of The Cochrane Library using the search term “pertussis” yielded five reviews, none of which were relevant.

Primary sources

A Medline search was performed using the following terms: (MeSH: Lymphocytosis OR MeSH: Lymphocyte Count OR “lymphocyte” OR “lymphocytosis” OR MeSH: Leukocytosis OR MeSH: Leukocyte count OR “leucocyte” OR “leukocyte” OR “leucocytosis” OR “leukocytosis” OR “white cell count” OR “full blood count” OR “complete blood count”) AND (MeSH: Whooping Cough OR pertussis OR “whooping cough”). Limits were: “Humans” and “English Language”.

The search yielded 414 individual articles. Eleven full text articles were examined, of which four were relevant; one further article was found …

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  • Competing interests None.

  • Provenance and peer review Not commissioned; externally peer reviewed.