Background 

A consensus definition recently was formulated for fracture-related infection, which centered on confirmatory criteria including conventional cultures that take time to finalize and have a 10% to 20% false-negative rate. During this time, patients are often on broad-spectrum antibiotics and may remain hospitalized until cultures are finalized to adjust antibiotic regimens.

Questions/purposes 

(1) What is the diagnostic accuracy of isothermal microcalorimetry, and how does its accuracy compare with that of conventional cultures? (2) Does isothermal microcalorimetry decrease time to detection (or diagnosis) of fracture-related infection compared with conventional cultures? (3) Does isothermal microcalorimetry have a diagnostic accuracy or time advantage over conventional cultures in patients on chronic suppressive antibiotics?

Methods 

Between July 2020 and August 2021, we treated 310 patients with concerns for infection after prior fracture repair surgery. Of those, we considered all patients older than 18 years of age with fixation hardware in place at the time of presentation as potentially eligible. All included patients returned to the operating room with cultures obtained and assessed by both isothermal microcalorimetry and conventional cultures, and all were diagnosed using the consensus criteria for fracture-related infection. Based on that, 81% (250 of 310) of patients were eligible; a further 51% (157 of 310) were excluded because of the following reasons: the capacity of the isothermal microcalorimetry instrument limited the throughput on that day (34% [106 of 310]), they had only swab cultures obtained in surgery (15% [46 of 310]), or they had less than 3 months follow-up after surgery for infectious concerns (2% [5 of 310]), leaving 30% (93 of 310) of the originally identified patients for analysis. We obtained two to five cultures from each patient during surgery, which were sent to our clinical microbiology laboratory for standard processing (conventional cultures). This included homogenization of each tissue sample individually and culturing for aerobic, anaerobic, acid-fast bacilli, and fungal culturing. The remaining homogenate from each sample was then taken to our orthopaedic research laboratory, resuspended in growth media, and analyzed by isothermal microcalorimetry for a minimum of 24 hours. Aerobic and anaerobic cultures were maintained for 5 days and 14 days, respectively. Overall, there were 93 patients (59 males), with a mean age of 43 ± 14 years and a mean BMI of 28 ± 8 kg/m², and 305 tissue samples (mean 3 ± 1 samples per patient) were obtained and assessed by conventional culturing and isothermal microcalorimetry. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of isothermal microcalorimetry to diagnose fracture-related infection were compared with conventional cultures using a McNemar test based on the consensus definition of fracture-related infection. This consensus criteria is comprised of two levels of certainty for the diagnostic variables. The first is confirmatory criteria, where infection is considered definitely present and includes the presence of fistula/sinus tract/wound breakdown, purulent drainage or the presence of pus, presence of microorganisms in deep tissue specimens on histopathologic examination, presence of more than five neutrophils/high-powered field by histopathologic examination (only for chronic/late onset cases), and identification of phenotypically indistinguishable pathogens by conventional culture from at least two separate deep tissue/implant specimens. The second is suggestive criteria in which further investigation is required to achieve confirmatory status. Fracture-related infection was diagnosed for this study to minimize subjectivity based on the presence of at least one of the confirmatory criteria as documented by the managing surgeon. When suggestive criteria were present without confirmatory criteria, patients were considered negative for fracture-related infection and followed further in clinic after surgical exploration (n = 25 patients). All 25 patients deemed not to have fracture-related infection were considered infection-free at latest follow-up (range 3 to 12 months). The time to detection or diagnosis was recorded and compared via the Mann-Whitney U test.

Results 

Using the consensus criteria for fracture-related infection, there were no differences with the numbers available between isothermal microcalorimetry and conventional cultures in terms of sensitivity (87% [95% confidence interval 77% to 94%] versus 81% [95% CI 69% to 89%]), specificity (100% [95% CI 87% to 100%] versus 96% [95% CI 79% to 99%]), PPV (100% [95% CI 90% to 100%] versus 98% [95% CI 89% to 99%]), NPV (74% [95% CI 60% to 84%] versus 65% [95% CI 52% to 75%]), or accuracy (90% [95% CI 83% to 96%] versus 85% [95% CI 76% to 91%]; p = 0.13). The concordance by sample between conventional cultures and isothermal microcalorimetry was 85%. Isothermal microcalorimetry had a shorter median (range) time to detection or diagnosis compared with conventional cultures (2 hours [0.5 to 66] versus 51 hours [18 to 147], difference of medians 49 hours; p < 0.001). Additionally, 32 patients used antibiotics for a median (range) duration of 28 days (7 to 1095) before presentation. In these unique patients, there were no differences with the numbers available between isothermal microcalorimetry and conventional cultures in terms of sensitivity (89% [95% CI 71% to 98%] versus 74% [95% CI 53% to 88%]), specificity (100% [95% CI 48% to 100%] versus 83% [95% CI 36% to 99%]), PPV (100% [95% CI 85% to 100%] versus 95% [95% CI 77% to 99%]), NPV (63% [95% CI 37% to 83%] versus 42% [95% CI 26% to 60%]), or accuracy (91% [95% CI 75% to 98%] versus 78% [95% CI 57% to 89%]; p = 0.17). Isothermal microcalorimetry again had a shorter median (range) time to detection or diagnosis compared with conventional cultures (1.5 hours [0.5 to 48] versus 51.5 hours [18 to 125], difference of medians 50 hours; p < 0.001).

Conclusion 

Given that isothermal microcalorimetry considerably decreases the time to the diagnosis of a fracture-related infection without compromising the accuracy of the diagnosis, managing teams may eventually use isothermal microcalorimetry—pending developmental improvements and regulatory approval—to rapidly detect infection and begin antibiotic management while awaiting speciation and susceptibility testing to modify the antibiotic regimen. Given the unique thermograms generated, further studies are already underway focusing on speciation based on heat curves alone. Additionally, increased study sizes are necessary for both overall fracture-related infection diagnostic accuracy and test performance on patients using long-term antibiotics given the promising results with regard to time to detection for this groups as well.

Level of Evidence 

Level II, diagnostic study.

中文翻译：

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与传统组织培养相比，等温微量热法缩短了骨折相关感染的诊断时间

背景 

最近针对骨折相关感染制定了一个共识定义，其核心是确认标准，包括需要时间才能完成的传统培养，并且有 10% 至 20% 的假阴性率。在此期间，患者通常服用广谱抗生素，并可能继续住院，直到最终确定培养结果以调整抗生素治疗方案。

问题/目的 

(1) 等温微量热法的诊断准确性如何？其准确性与常规培养相比如何？(2) 与传统培养相比，等温微量热法是否会缩短骨折相关感染的检测（或诊断）时间？(3) 对于长期服用抑制性抗生素的患者，等温微量热法是否比传统培养具有诊断准确性或时间优势？

方法 

2020 年 7 月至 2021 年 8 月期间，我们治疗了 310 名在先前骨折修复手术后担心感染的患者。其中，我们认为所有年龄超过 18 岁且在就诊时已安装固定硬件的患者都可能符合资格。所有纳入的患者均返回手术室，并通过等温微量热法和常规培养获得和评估培养物，并且所有患者均使用骨折相关感染的共识标准进行诊断。基于此，81%（310 名患者中的 250 名）符合资格；另外 51%（310 人中的 157 人）因以下原因被排除：等温微量热仪的容量限制了当天的通量（34%（310 人中的 106 人）），他们仅获得了手术中获得的拭子培养物（15 % [310 人中的 46 人]），或者他们因感染问题进行手术后随访时间少于 3 个月（2% [310 人中的 5 人]），留下 30%（310 人中的 93 人）进行分析。我们在手术期间从每位患者身上获得了两到五种培养物，并将其送往我们的临床微生物实验室进行标准处理（常规培养物）。这包括对每个组织样本进行单独均质化以及需氧、厌氧、抗酸杆菌和真菌培养。然后将每个样品剩余的匀浆带到我们的骨科研究实验室，重新悬浮在生长培养基中，并通过等温微量热法进行至少 24 小时的分析。需氧和厌氧培养物分别维持5天和14天。总体而言，共有 93 名患者（59 名男性），平均年龄为 43 ± 14 岁，平均 BMI 为 28 ± 8 kg/m ²，并通过常规培养和等温微量热法获得并评估了 305 个组织样本（平均每个患者 3 ± 1 个样本）。根据骨折相关感染的共识定义，使用 McNemar 检验将等温微量热法诊断骨折相关感染的敏感性、特异性、阳性预测值 (PPV)、阴性预测值 (NPV) 和准确性与传统培养进行比较。该共识标准由诊断变量的两个确定性级别组成。第一个是确诊标准，其中感染被认为肯定存在，包括存在瘘管/窦道/伤口破裂、化脓性引流或存在脓液、组织病理学检查深部组织标本中存在微生物、存在超过五个中性粒细胞/通过组织病理学检查（仅适用于慢性/迟发病例）进行高倍视野，并通过至少两个单独的深层组织/植入标本的常规培养来鉴定表型难以区分的病原体。第二个是建议性标准，需要进一步调查才能达到确认状态。本研究根据主治外科医生记录的至少一项确认标准来诊断骨折相关感染，以尽量减少主观性。当存在提示性标准而没有确认性标准时，患者被认为骨折相关感染呈阴性，并在手术探查后在临床进行进一步随访（n = 25 名患者）。所有 25 名被认为没有骨折相关感染的患者在最近一次随访（3 至 12 个月）时均被视为无感染。通过 Mann-Whitney U 检验记录并比较检测或诊断的时间。

结果 

使用骨折相关感染的共识标准，等温微量热法和传统培养之间的可用数字在敏感性方面没有差异（87% [95% 置信区间 77% 至 94%] 对比 81% [95% CI 69] % 至 89%]）、特异性（100% [95% CI 87% 至 100%] 与 96% [95% CI 79% 至 99%]）、PPV（100% [95% CI 90% 至 100%]）与 98% [95% CI 89% 至 99%]）、NPV（74% [95% CI 60% 至 84%] 与 65% [95% CI 52% 至 75%]）或准确度（90% [ 95% CI 83% 至 96%] 与 85% [95% CI 76% 至 91%]；p = 0.13）。常规培养和等温微量热法之间的样品一致性为 85%。与传统培养相比，等温微量热法的检测或诊断时间中位（范围）较短（2 小时 [0.5 至 66] 与 51 小时 [18 至 147]，中位差 49 小时；p < 0.001）。此外，32 名患者在就诊前使用抗生素的中位（范围）持续时间为 28 天（7 至 1095 天）。在这些独特的患者中，等温微量热法和传统培养之间的可用数字在灵敏度方面没有差异（89% [95% CI 71% to 98%] vs 74% [95% CI 53% to 88%]） 、特异性（100% [95% CI 48% 至 100%] 对比 83% [95% CI 36% 至 99%]）、PPV（100% [95% CI 85% 至 100%] 对比 95% [95%] CI 77% 至 99%]）、NPV（63% [95% CI 37% 至 83%] 与 42% [95% CI 26% 至 60%]）或准确度（91% [95% CI 75% 至 60%]） 98%] 与 78% [95% CI 57% 至 89%]；p = 0.17）。与传统培养相比，等温微量热法的检测或诊断中位（范围）时间再次较短（1.5 小时 [0.5 至 48] 与 51.5 小时 [18 至 125]，中位差异 50 小时；p < 0.001）。

结论 

鉴于等温微量热法大大缩短了骨折相关感染的诊断时间，且不影响诊断的准确性，管理团队最终可能会使用等温微量热法（等待发展改进和监管部门批准）来快速检测感染并在等待时开始抗生素管理形态和药敏试验以修改抗生素治疗方案。鉴于生成的独特热分析图，进一步的研究已经在进行中，重点关注仅基于热曲线的形态形成。此外，鉴于骨折相关感染的总体诊断准确性和长期使用抗生素的患者的测试性能，增加研究规模是必要的，因为该组在检测时间方面也取得了有希望的结果。

证据水平 

第二级，诊断研究。