The results of Legionella urinary antigen testing were correlated to t
he interval between onset of disease and sampling of urine in 134 pati
ents in connection with a large outbreak of Legionnaires' disease al a
Swedish hospital. In 17 patients with the disease, 5/7 sampled during
the first 5 days of illness proved negative in the urinary antigen te
st. The risk of obtaining negative results during the first days of th
e disease is emphasized.