Infection (either community acquired or nosocomial) is a major cause of morbidity and mortality in critical care medicine. Sepsis is present in up to 30% of all ICU patients. A large fraction of sepsis cases is driven by severe community acquired pneumonia (sCAP), which incidence has dramatically increased during COVID-19 pandemics. A frequent complication of ICU patients is ventilator associated pneumonia (VAP), which affects 10–25% of all ventilated patients, and bloodstream infections (BSIs), affecting about 10% of patients. Management of these severe infections poses several challenges, including early diagnosis, severity stratification, prognosis assessment or treatment guidance. Digital PCR (dPCR) is a next-generation PCR method that offers a number of technical advantages to face these challenges: it is less affected than real time PCR by the presence of PCR inhibitors leading to higher sensitivity. In addition, dPCR offers high reproducibility, and provides absolute quantification without the need for a standard curve. In this article we reviewed the existing evidence on the applications of dPCR to the management of infection in critical care medicine. We included thirty-two articles involving critically ill patients. Twenty-three articles focused on the amplification of microbial genes: (1) four articles approached bacterial identification in blood or plasma; (2) one article used dPCR for fungal identification in blood; (3) another article focused on bacterial and fungal identification in other clinical samples; (4) three articles used dPCR for viral identification; (5) twelve articles quantified microbial burden by dPCR to assess severity, prognosis and treatment guidance; (6) two articles used dPCR to determine microbial ecology in ICU patients. The remaining nine articles used dPCR to profile host responses to infection, two of them for severity stratification in sepsis, four focused to improve diagnosis of this disease, one for detecting sCAP, one for detecting VAP, and finally one aimed to predict progression of COVID-19. This review evidences the potential of dPCR as a useful tool that could contribute to improve the detection and clinical management of infection in critical care medicine.

Bloodstream infections (BSIs) caused by bacteria associated with sepsis are among the leading causes of mortality, particularly in critically ill patients. The gold standard method for the microbiological diagnosis of BSIs is still blood culture, which is slow, cannot detect viruses, and only yield positive results in one-third of suspected BSIs and sepsis cases. Droplet digital PCR (ddPCR) is a next-generation PCR method, with great precision and accuracy, that allows absolute quantification of target gene(s) without a standard curve and little interference from normal PCR inhibitors. These characteristics make ddPCR an ideal method for the detection and quantification of pathogens directly from blood or other clinical samples in patients with suspected BSI and sepsis. The aim of this work was to use genus/species specific genes ddPCR assays to detect and quantify bacterial DNA from four of the most common BSIs pathogens in blood. Here we demonstrate the quantification capacity and specificity of two duplex ddPCR assays that allow the detection and quantification of Escherichia coli, Klebsiella pneumoniae, Staphylococcus aureus and Enterococcus spp directly from blood.