The Duke criteria identify S aureus bacteremia as a major criterion, regardless of whether the infection was nosocomial or com- munity acquired or whether a primary source of infection was present or absent.75 suggests that the presence of a CVC may skew the diagnosis of IE, because the attempt to salvage the catheter rather than remove it serves to prolong the bacteremic state and raises the question of whether S aureus bacteremia should be regarded as a major microbiological cri- teria only if cultures remain positive after removal of the CVC. Laboratory Assessment Microbiology: Blood Cultures Blood cultures should be drawn for patients with fever of unexplained origin and a pathological heart murmur, a history of heart disease, or previous endocarditis. Because bactere- mia in patients with IE usually is continuous and low grade, it does not matter whether cultures are obtained at any particular phase of the fever cycle. For children, it is ordinarily not prac- tical to obtain the large volumes recommended for adults with suspected endocarditis. Lesser amounts (eg, 1 3 mL in infants and young children and 5 7 mL in older children) are optimal, depending on the blood culture detection system. Because IE is only rarely caused by anaerobic bacteria, emphasis is usu- ally given to inoculating blood into bottles for aerobic incuba- tion. It is reasonable to obtain 3 blood cultures by separate venipunctures on the first day, and if there is no growth by the second day of incubation, to obtain 2 or 3 more (Table 3). There is usually no value in obtaining >5 blood cultures over 2 days unless the patient has received antibiotic therapy within the past 2 weeks. 