Figure 1. Patient 1. A child whose matching bronchoalveolar lavage (BAL) samples, throat swabs and sera were available annually for three of four years of monitoring. This child had no prior history of P. aeruginosa and the BAL and throat swabs remained P. aeruginosa culture negative for samples obtained in year one and two of the observation period. However, in year four the child developed a persistent cough and a throat swab was culture positive for P. aeruginosa, while a simultaneously collected BAL sample grew low numbers of P. aeruginosa (10² colony forming units/ml) and demonstrated signs of increased airway inflammation.