A child with complaints of cough. Characteristic inspiratory whoop present. Not immunised. Sample for investigation is ?

Nasopharyngeal swab Characteristic inspiratory stridor in a child suggests whooping cough. About the diagnosis of whooping cough "Though the disease is mainly in the lower respiratory tract the organism can be rapidly isolated from nasopharyngeal swab". Diagnosis of peussis Peussis can be easily diagnosed clinically because of its characteristic symptoms. If the classical symptoms of peussis are present clinical diagnosis is not difficult. Because atypical clinical cases occur frequently, laboratory confirmation of the diagnosis is often essential. Laboratory confirmation :- Lymphocvtosis A peculiar feature of Bordetella infection is "lymphocytosis" (lymphocytosis is unusual in bacterial infections). - M bordetella an absolute lymphocyte count of >10 x 109/L is common among young children. - Although lymphocytosis is characteristic response to peussis infection, many cases of true peussis infection do not develop a significant increase in circulating lymphocytes, conversely there are so many causes of lymphocytosis that a positive result lacks diagnostic specificity.