mNGS for Therapy of Urinary Infectious Diseases

Urinary tract infection is a common infectious disease in clinic. Urinary tract infection is easily caused by abnormal structure and function of urinary system, low immunity, pregnancy, gender and sexual activity, and iatrogenic factors. Urinary tract infection has a wide spectrum of pathogenic microorganisms, including Gram-negative bacilli, Gram-positive cocci, fungi, mycoplasma, chlamydia, viruses and so on. Although urinary tract infection can be initially diagnosed by clinical sign and symptom, signs and urine routine, the application of appropriate antibiotic therapy depends on the further identification of pathogens. At present, it is commonly used to collect midstream urine for pathogen culture in clinic, but it has the disadvantages of time-consuming and low detection rate, and the use of antibiotics can affect the results of culture.

Metagenomic sequencing has been widely used in clinical pathogen diagnosis, especially in difficult infectious diseases. Its principle is to collect samples, use mNGS to process the samples before sequencing, expose the nucleic acid, compare the nucleic acid sequence of pathogens with the designated huge biological database, and realize the comprehensive detection of viruses, bacteria, fungi, parasites and atypical microorganisms. Compared with tissue samples, cerebrospinal fluid, bronchoalveolar lavage fluid, whole blood and other samples, the application of mNGS in urine samples is relatively limited because incorrect sampling methods before and after collection of urine samples are easy to contaminate the samples and the colonization of distal urethra, periurethral skin and vagina will interfere with the interpretation of reports. However, mNGS has obvious advantages in clinical diagnosis, with high specificity and accuracy, and shorter detection time than traditional culture. In the aspect of mixed infection, because of its non-bias, the detection rate of multiple pathogens is higher than that of conventional culture, smear, PCR and other tests, which can detect other pathogens and even rare pathogens that can not be detected conventionally.

Previous small sample studies have shown that the sensitivity of mNGS in urinary tract infection is high, but the specificity is relatively low, and there are many problems such as difficult interpretation of reports and low clinical conformity. For example, there are many pathogens with high reading, and the test results are sorted to form a list of pathogens, but it is impossible to determine which or which pathogens are pathogenic. This is closely related to the mNGS technology algorithm, such as the inability to eliminate the influence of urinary system background bacteria, and the ambiguity of short sequence alignment, which makes it difficult to distinguish homologous pathogens.

In this study, based on the standard mNGS sequencing process, the improved Z value analysis method was used to select strictly enrolled clinical samples and compare them with pathogen culture to observe the clinical value of mNGS with Z value analysis method in the treatment of urinary tract infection.