Cell – free DNA (cfDNA) blood collection tubes have the following important applications in infectious disease detection:

I. Pathogen Detection

1. Virus Detection
   • Viral Load Monitoring
     During a viral infection, the virus replicates within host cells, and part of the viral nucleic acid is released into the bloodstream in the form of cell – free DNA (cfDNA). By collecting blood with cfDNA blood collection tubes, nucleic acid detection techniques such as real – time fluorescence quantitative PCR can be used to quantitatively analyze the viral cfDNA in the blood, thus monitoring the viral load. For example, in human immunodeficiency virus (HIV) infection, detecting the cfDNA load of HIV – 1 virus in the blood can help doctors understand the replication status of the virus in the patient. This is crucial for assessing disease progression, formulating antiretroviral treatment plans, and monitoring treatment efficacy.
   • Virus Genotyping
     Different genotypes of viruses may vary in pathogenicity, transmissibility, and drug sensitivity. Using the cfDNA in the blood samples collected by the blood collection tubes, the genotype of the virus can be determined through techniques such as gene sequencing. Taking hepatitis C virus (HCV) as an example, detecting its cfDNA can identify the viral gene subtype. This helps doctors select the most effective antiviral drugs for patients, as different gene subtypes of HCV may respond differently to drugs.
   • Discovery of New Viruses
     In the early stage of an epidemic outbreak or in cases of unknown pathogen infections, the blood samples collected by cfDNA blood collection tubes can serve as important testing materials. Through techniques such as metagenomic sequencing of the cfDNA in the blood, the presence of new viruses can be discovered. For example, in the early stage of the COVID – 19 pandemic, scientists detected and analyzed the cfDNA in samples such as the blood of patients, which assisted in identifying the presence of the novel coronavirus (SARS – CoV – 2) and further understanding its genetic characteristics.
2. Bacteria Detection
   • Diagnosis of Bacteremia
     When bacteria enter the bloodstream and multiply, it causes bacteremia. The blood samples collected by cfDNA blood collection tubes can be used to detect the cfDNA released by bacteria. By detecting the gene sequences of specific bacteria, bacteremia can be diagnosed rapidly. For example, for bacteremia caused by Staphylococcus aureus, detecting the presence of Staphylococcus aureus cfDNA in the blood can help doctors initiate effective antibacterial treatment in a timely manner, improving the survival rate of patients.
   • Monitoring of Bacterial Antibiotic Resistance
     With the widespread use of antibiotics, the problem of bacterial antibiotic resistance is becoming increasingly serious. By detecting the cfDNA of bacteria in the blood, the antibiotic – resistant genes of bacteria can be analyzed. For example, detecting the carbapenemase – resistant genes in the cfDNA of Klebsiella pneumoniae can help understand the antibiotic – resistant situation of bacteria in advance. This can guide clinicians to rationally select antibiotics, avoid using ineffective antibiotic treatments, and reduce the spread of drug – resistant bacteria.

II. Disease Monitoring and Prognosis Assessment

1. Monitoring of Disease Activity
   During the course of an infectious disease, the changes in the content of pathogen cfDNA in the blood can reflect the degree of disease activity. For example, in patients with infectious mononucleosis (caused by Epstein – Barr virus), by regularly collecting blood to detect the level of Epstein – Barr virus cfDNA, it can be determined whether the disease is in an active stage. When the cfDNA content increases, it may indicate active viral replication and increased disease activity; while a decrease in cfDNA content may suggest that the disease is under control.
2. Prognosis Assessment
   The test results of pathogen cfDNA in the blood are also of great value for the prognosis assessment of infectious disease patients. Taking viral hepatitis as an example, if the viral cfDNA in the patient’s blood continues to decline and eventually turns negative during the treatment process, this is usually a good prognostic sign, indicating that the treatment is effective and the patient has a high likelihood of recovery. Conversely, if the cfDNA remains at a high level or rebounds, it may indicate a poor prognosis, such as the possible development of chronic hepatitis, liver cirrhosis, and other serious consequences.