影響血液培養系統陽性率的因子探討

Factors Affecting the Recovery of Microorganisms from Blood Culture Systems

探討BacT/Alert血液培養自動偵測系統在培養時間之必要性與厭氧瓶重要性之分析外，同時評估開立第二與第三套血瓶的價值。在2,959瓶陽性血瓶中，其中2,933瓶（99.1%）在5天內陽性、另外的23瓶與3瓶（0.8%與0.1%）分別在第6與7天呈陽性培養。26瓶中只有8瓶被認為有意義，包括3株Klebsiella pneumoniae （127~142小時），2株Staphylococcus aureus （120-137小時），1株Serratia marcescens （135小時），1株Burkholderia cepacia （132小時）以及1株non-enterococcus （130小時）。因此，血液培養自動偵測系統置放至第六天與第七天已無太大意義。在20,908瓶（10,454套）成人血液培養瓶中，若排除革蘭氏陽性桿菌與稀有分離菌，共有1,740套（2,695瓶）為陽性。其中30.1%（523套／1,740套）僅需氧瓶有長，另外15.1% （262套／1,740套）僅需厭氧瓶有長，54.8%（955套／1,740套）需氧與厭氧皆長。對於厭氧菌的分離，1.94% （7/36）厭氧菌僅長在需氧瓶，75%（27/36）厭氧菌僅長在厭氧瓶，另外5.6%（2/36）厭氧菌在需氧與厭氧瓶皆能生長。30.4%（290/955）厭氧瓶陽性速度快於需氧瓶，因此若未接種厭氧瓶將減少厭氧菌分離率與報告時效。再就21,112血瓶中，2,959瓶為陽性，包括1,381個（2,618瓶）擬分析的個案以及341瓶不擬分析的革蘭氏陽性桿菌與稀有菌株。擬分析的個案包含了779個開立一套血瓶培養、446個開立兩套不同時段的血瓶培養以及115個開立三套或三套以上之血瓶培養。兩套培養皆陽性的機率為50.9%（227/446），僅第一套陽性之機率是28.2%（126/446），僅第二套陽性之機率為20.9%（93/446）。再就115個開立三套培養而言，其中第一套血瓶是陰性的比率佔了14.8%（17/115）。因此開立超過一套的血液培養可增加10-20%的陽性機率。

We evaluate the incubation time and anaerobic bottles for efficient detection of microorganisms by a blood culture system. BacT/Alert, and consider the values of second and third sets of blood cultures. Of the 2,959 positive vials, 2,933 vials (99.1%) were positive in the first five days of testing; 23 and 3 vials (0.8 and 0.1%) were positive on day 6 and 7. Only 8 of the latter vials were judged to contain significant strains: three Klebsiella pneumoniae (127-142hr), two Staphylococcus aureus (120-137hr), one Serratia marcescens (135hr), one Burkholderia cepacia (132hr) and one non-enterococcus (130hr). The data suggested that the clinical benefit of testing on days 6 and 7 does not justify its cost in our patient population. Among 20,908 blood culture vials processed from adults, there were 2,695 positive vials from 1,740 sets not inclusive of Gram positive bacillus and few isolation strains. 30.1% (523/1,740) sets grew only in the aerobic bottles,another 15.1% (262/1,740)sets did so only in the anaerobic bottles. For the isolation of anaerobes, 19.4%(7/36) anaerobes grew in aerobic vials only and 75% (27/36) grew positive only in anaerobic bottles and 5.6% (2/36) both vials positive. 30.4% (290/955) anaerobic bottle grew earlier than the aerobic bottle. My findings suggested that omitting the use of the anaerobic blood culture vial will seriously compromise the recovery of some anaerobes and will delay blood culture reports. Among 21,112 blood culture vials, 2,959 vials yielded positive results. Among positive cultures, 1,381 episodes (2,618 vials) were further identified. Gram-positive bacilli were suspected in 341 vials and were not studied further. Among the 1,381 episodes, 779 episodes were diagnosed with one set of blood culture, 446 episodes with two sets and 115 episodes with three or more at intervals. Among the 446 episodes diagnosed with two sets, 50.9% (227/446) were test positive in both sets,while 28.2% (126/446) were positive in the first set and 20.9% (93/446) were positive in the second set of cultures. Among the 115 episodes by three sets, the first set was negative in 14.8% (17/115).Our data demonstrates a 10-20% improvement of detection sensitivity when more than one blood speciment is repuested.