Patient characteristics and pathogen detection
One hundred and forty patients with a 67.9% male to female ratio and a mean age of 55.8 years were enrolled at four hospitals. Fever or hypothermia was the most frequent symptom observed (77.9%), followed by change in mental status (22.1%), focal pain or dysfunction (18.6%), and cough (17.1%). Most patients (92.8%) came from Intensive Care Units or Departments of Infectious Disease. A total of 92.9% of patients received antimicrobial treatment in the two weeks prior to mNGS examination. The following samples were collected for mNGS testing from patients recruited for the study: peripheral blood (110 patients), bronchoalveolar lavage fluid (BALF) (24 patients), cerebrospinal fluid (CSF) (32 patients), and other types, e.g., sputum, pleural fluid, ascites, and pericardial effusion (29 patients) (Fig. 1A).
Seventy-one patients have detected a potential pathogen (environmental microbes which considered as contaminants were filtered), of which bacteria, fungi and virus accounted for 65%, 10% and 10%, respectively. In addition, 15% of patients may have combined infection (Fig. 1B).
A total of 115 out of 140 patients received a final diagnosis of infection; pneumonia was the most common (66.1%, 76/115), followed by infections of the central nervous system (19.3%, 26/115) and bloodstream (13.9%, 16/115). Twenty-five patients (21.7%) had more than one source of infection. The positive mNGS tests of 61 patients were assessed to be clinically relevant. The sensitivity and specificity of mNGS testing for diagnosis of a clinically relevant infection was 53.0% (61/115) and 60% (15/25), respectively, vs 20.9% (24/115) and 96.0% (24/25), respectively, for conventional microbiological testing (both P < 0.01). Klebsiella pneumoniae was the most common pathogen detected by mNGS, followed by E. coli and viruses.
Integrate copy number variation analysis with mNGS
The main objective of the current study was to explore the possibility of using mNGS to detect malignant tumors. Inasmuch as the experimental approach is consistent with current methods of mNGS library preparation, a new analysis workflow (Onco-mNGS) is proposed here for using homo reads data to search for evidence of malignant tumors (Fig. 2A). A process was established based upon the read counting strategy.
This process was tested first using known pathologic samples. Standard diploid samples with no chromosomal deletions or duplications were obtained from healthy individuals (Fig. 2B). In contrast, dramatic chromosome disorders were observed in tumor tissues obtained from two colorectal cancer patients. Considering the proportion of tumor cells in the samples could be low, the sensitivity of the method was further examined by preparing and testing a variety of samples with different tumor to normal cell ratios (Supplementary Fig. S1). Chromosome abnormalities were readily detected at ratios of 5–20% supporting the overall concept of using mNGS technologies to identify malignant tumors. These results support the feasibility of integrating CNV analysis with mNGS to detect tumors.
Analysis of homo reads for tumor clues
Next, CNV analysis was performed on each study sample. The homo read ratios were calculated for the three major sample types: peripheral blood, BALF and CSF. The average ratio of homo reads for each sample type was > 95% (plasma: 96.26%; BALF: 96.03%; CSF: 95.84%) (Fig. 3A). After excluding microbial sequences, ≥ 8 million homo reads were obtained for each sample, enough to conduct CNV analysis. Seventeen samples with significant chromosomal disorders were identified. Among these, ten were peripheral blood and seven were body fluid samples (three BALF, two pleural fluid, and two CSF). Abnormal CNV signals were observed in both peripheral blood and BALF samples obtained from one patient (#12).
The following chromosome abnormalities were observed in these 17 patients: 1) genome-wide multiple chromosome duplication and deletion in 10 patients (#s 1, 2, 3, 4, 5, 10, 11, 13, 16 and 17); 2) arm level duplication and deletion in four patients (#s 6, 8, 9, 14); 3) loss of chromosome Y in two patients (#s 7 and 12); and 4) chromosome aneuploidy in one patient (# 15) (Fig. 3B and Supplementary Fig. S2). The genome-wide chromosome abnormality was observed to be the most type of CNV variation (Fig. 3D).
Clinical validation of Onco-mNGS
Ten peripheral blood samples were obtained from these 17 patients. Additionally, tumor-like signals were found in body fluid samples (three BALF, two pleural fluid, and two CSF). Six patients with obvious, abnormal CNV signals had no recorded history of malignant tumors prior to Onco-mNGS. Malignant tumors were subsequently confirmed in five patients (#s 1–5). Three lung adenocarcinomas and two hematological tumors were determined by pathologic examination of tissues obtained by bone marrow biopsy, bone biopsy or surgery after the results of Onco-mNGS analysis were reported to the attending physicians (Fig. 3C and Table 1). The remaining patient (#6) was suspected of having central nerve system lymphoma, but refused to undergo a biopsy prior to death (Table 1 and Fig. 3).
Table 1
Clinical characteristics of patients with CNV changes and no history of malignancy before mNGS testing
No. | Sex, year | History of malignancy | Diagnosis of admission | Diagnosis of discharge | Symptom | Prior antimicrobial agents use | Onco-mNGS | Conventional method |
Pathogen detected | CNVs | Days to diagnosisa | Culture result | Pathology detected | Days to diagnosis |
1 | Female, 58 | None | Thoracic vertebrae lesion | Diffuse large B cell lymphoma | Chest and back pain | Vancomycin; Fosfomycin | None | Multiple Chrsb Del/Dup | 14 days | None | Bone biopsy: diffuse large B cell lymphoma | 46 days |
2 | Male, 67 | None | Liver abscess | Lung cancer; Liver occupation; Pneumonia | Fever; Change in metal status | Meropenem; Ciprofloxacin; Linezolid; | None | Chr2 Dup | 90 days | None | Bronchoscope: neoplasm in superior segmental bronchus Pathology: adenocarcinoma | 98 days |
3 | Male, 23 | None | Fever of unknown origin | NK T cell lymphoma | Fever; Vomit | Meropenem; Doxycycline; Vancomycin; Cefoperazone; Sulbactam | Blood: Bacillus thuringiensis | Multiple Chrs Del/Dup | 6 days | None | Bone marrow smear: NK T cell lymphoma | 71 days |
4 | Female, 71 | None | Lung lesion | Lung cancer | Cough; Sputum | None | None | Multiple Chrs Del/Dup | 9 days | None | Lung biopsy: adenocarcinoma | 20 days |
5 | Male, 71 | None | Pericardial and pleural effusion | Lung cancer | None | Moxifloxacin | None | Multiple Chrs Del/Dup | 5 days | None | Lung biopsy: adenocarcinoma | 10 days |
6 | Male, 69 | None | Encephalitis possible | Central lymphoma possible | Fever; Change in metal status | Ceftriaxone; Metronidazole | CSF: Elizabethkingia anophelis | Chr9q Dup | 29 days | None | - | - |
aDuration of time between the first day of hospitalization and the report of Onco-mNGS or pathological results. |
bAbbreviations: Chr, chromosome; Dup, duplication; Del, deletion |
The remaining 11 patients(#s 7–17)with obvious abnormal CNV signals had a history of malignant tumors noted upon chart review (Supplementary Table S1 and Fig. S2). Hematologic tumors were the most frequently detected accounting for 63.6% of the malignant tumors. In this study, 30 of 140 patients in this study had a history of malignancy before Onco-mNGS analysis; 19 of these patients, however, were not found to have obvious abnormal CNV signals.
By combining the mNGS analyses with CNV analyses, 12 of the 17 patients with obvious abnormal CNV signals were found to have negative mNGS results, indicating malignant tumor may be the cause of infection-like symptoms such as fever (Fig. 3E).
Case vignettes in which Onco-mNGS yielded a malignant diagnosis
Case 1
Diffuse large B cell lymphoma. A 58-year-old female presented after 2 months with right chest and back pain with no fever (Fig. 4A). A CT scan revealed destruction of the 9th thoracic vertebra and the right appendix with paravertebral soft tissue shadow (Fig. 4B). Magnetic resonance imaging (MRI) revealed abnormal signals of the 9th thoracic vertebra and right arch with swelling of the surrounding soft tissue. Pathologic results of the bone biopsy indicated infection. The patient was treated empirically with vancomycin and fosfomycin (switched to linezolid due to nausea and vomiting) administered i.v. for 3 weeks. The patient developed paralysis of the lower extremities and difficulty urinating. Repeated MRI showed that the lesion had become significantly larger with spinal compression.
Onco-mNGS analysis failed to detect microorganisms in her peripheral blood, but revealed deletions and duplications of large segments in several chromosomes that generated a strong abnormal CNV-based tumor signal (Fig. 4C). This finding encouraged treating physicians to obtain a second bone biopsy; the result revealed diffuse large B cell lymphoma of the non-germinal center B cell type (Fig. 4D). The patient received R-CHOP chemotherapy afterwards and the symptoms were mildly relieved. The fluctuation in chromosomal variation was much smoother in the fourth, compared to previous, Onco-mNGS tests suggesting that the proportion of tumor cells had decreased.
Case 2
NK/T cell lymphoma. A 23-year-old male presented after 2 weeks of fever and vomiting. Upon admission, the patient exhibited a low platelet count (45⋅109/L) and elevated levels of inflammatory markers (C-protein: >199 mg/L; procalcitonin: 13.92 ng/mL). Tests for pathogens that included Epstein-Barr virus (EBV), cytomegalovirus (CMV), cryptococcus, tuberculosis, and parasites were negative; blood cultures for bacteria, acid-fast bacilli, and fungi were also negative. A PET-CT scan showed an enlarged spleen with increased uptake of FDG indicator. The patient underwent two diagnostic bone marrow punctures and a splenectomy; the results, however, did not support a definitive diagnosis. The patient was treated empirically with meropenem, vancomycin, doxycycline, gentamycin, and trimethoprim/sulfamethoxazole administered sequentially, but became worse with progressive hepatic deterioration (total bilirubin: 356.4 µmol/L). The results of a third bone marrow biopsy revealed NK/T cell lymphoma.
Onco-mNGS results showed disruptions in several chromosomes indicative of a tumor. This was confirmed by the results of a third bone marrow smear. Unfortunately, this information was not considered a priori by the attending physicians and the patient soon died of tumor progression. Although the diagnostic information provided by Onco-mNGS did not impact the clinical outcome of this patient directly, the case illustrates the potential benefits of this approach to patients with fever of unknown origin. It substantially shortens the time required for diagnosis and should eliminate unnecessary antimicrobial treatment.
Case 3
Lung adenocarcinoma. A 71-year-old female presented after 2 months of cough and sputum, but no fever. Her chest CT scan showed pneumonia; Mycoplasma pneumoniae-specific IgM antibody was positive. She was treated with cefuroxime and azithromycin administer i.v. for 6 days, then switched to oral moxifloxacin for 10 days. The patient did not improve in clinical or radiological presentation. Repeated, M. pneumoniae serum antibody was negative. Bronchoscopy was conducted, but tests for pathogens including bacteria, acid-fast bacteria, and fungi in BALF were negative. The patient received a pulmonary lobectomy and the pathological result indicated lung adenocarcinoma.
Tumor markers in this patient, i.e., CA199, CEA, CA125, CY211 and SCC, were in the normal range. A quick tumor diagnosis was overlooked since pneumonia was considered first. The Onco-mNGS result showed no microorganisms, but likely tumor signals. This finding supported the clinical decision to cease antimicrobial treatment and persuade the patient to receive invasive operations, which led to the final diagnosis.