Soft salt-mannitol agar-cloxacillin test: a highly specific bedside screening test for detection of colonization with methicillin-resistant Staphylococcus aureus.
The early detection of colonization with methicillin-resistant Staphylococcus aureus (MRSA) of patients in intensive-care units is an essential step in the strategy for preventing MRSA epidemics. In this study, tubes containing soft salt-mannitol agar with cloxacillin (6 microg/ml) (SSMAC) were prepared for inoculation of clinical samples at patients' bedsides by personnel of an intensive-care unit. A total of 1,914 swabs from different sample sites of 81 patients were dipped into SSMAC tubes, and after 24 h of incubation (in an incubator located near the intensive-care unit), an evident color change was considered by the intensive-care-unit personnel to be an MRSA alarm. Sixty-three (3.3%) SSMAC tubes were considered positive for MRSA, 1,827 (95.4%) were considered negative, and 24 (1.2%) were considered intermediate. Compared with values for parallel conventional surveillance cultures for MRSA, excluding tubes with intermediate results, the SSMAC test had a sensitivity of 72.7%, a specificity of 99.2%, a positive predictive value of 76.2%, and a negative predictive value of 99.0%. When intermediate tubes were considered positive, the corresponding values were 75.3, 98.2, 63.2, and 99.0%, respectively. The sensitivity and specificity values of the test to identify MRSA-colonized patients were 89.4 and 100%, respectively. Oropharyngeal and naris specimens were the most reliable samples for MRSA detection. False-negative results were frequent in bronchial aspirates with low (< 10(3) to 10(6) CFU/ml) MRSA counts. False-positive results were mainly due to methicillin-resistant Staphylococcus haemolyticus. The SSMAC tube is a useful, rapid, and inexpensive tool for the early identification of MRSA-colonized patients and, consequently, for the implementation of measures to prevent the spread of MRSA.
Mir
N
N
Servicio de Microbiología, Hospital Ramón y Cajal, Madrid, Spain.
Sánchez
M
M
Baquero
F
F
López
B
B
Calderón
C
C
Cantón
R
R
D000328:Adult; D000362:Agar; D000368:Aged; D000369:Aged, 80 and over; D003023:Cloxacillin / Q000494:pharmacology*; D006801:Humans; D008353:Mannitol / Q000494:pharmacology*; D016106:Methicillin Resistance; D008875:Middle Aged; D010406:Penicillins / Q000494:pharmacology*; D012680:Sensitivity and Specificity; D012965:Sodium Chloride / Q000494:pharmacology*; D013211:Staphylococcus aureus / Q000302:isolation & purification*
D010406:Penicillins; D008353:Mannitol; D012965:Sodium Chloride; D000362:Agar; D003023:Cloxacillin