The correct answer is D. You answered D.

The answer is D.(Chap. 184)Legionella urine antigen is detectable within 3 days of symptoms and will remain positive for 2 months. It is not affected by antibiotic use. The urinary antigen test is formulated to detect only L pneumophilia (which causes 80% of Legionella infections), but cross-reactivity with other Legionella species has been reported. The urinary test is sensitive and highly specific. Typically, Gram staining of specimens from sterile sites such as pleural fluid show numerous WBCs but no organisms. However, Legionella may appear as faint, pleomorphic gram-negative bacilli. Legionella may be cultured from sputum even when epithelial cells are present. Cultures, grown on selective media, take 3–5 days to show visible growth. Antibody detection using acute and convalescent serum is an accurate means of diagnosis. A fourfold rise is diagnostic, but this takes up to 12 weeks and thus is most useful for epidemiologic investigation. Legionella PCR has not been shown to be adequately sensitive and specific for clinical use. It is used for environmental sampling.