Background: Co-infections, secondary bacterial or fungal infections, are important risk factors for poor outcomes in viral infections. The prevalence of co-infection and secondary infection in patients infected with SARS-CoV-2 is not well understood. Aims: To investigate the role of co-infections and secondary infections in disease severity of hospitalized individuals with COVID-19. Materials and Methods: A retrospective study was carried out between 11 January 2020 and 1 March 2020 among 408 laboratory confirmed COVID-19 patients in China. These patients were divided into three groups based on disease severity: mild or moderate, severe, or critically ill. Microbiological pathogens in blood, urine, and respiratory tract specimens were detected by the combination of culture, serology, polymerase chain reaction, and metagenomic next-generation sequencing (mNGS). Results: The median age of participants was 48 years (IQR 34-60 years). Fifty-two patients (12.7%) had at least one additional pathogen, 8.1% were co-infected, and 5.1% had a secondary infection. There were 13 Mycoplasma pneumoniae cases, 8Haemophilus influenzae cases, 8 respiratory viruses, and 3 Streptococcus pneumoniae cases, primarily detected in mild and moderate COVID-19 patients. Hospitalacquired infection pathogens were more common in critically ill patients. Compared to those without additional pathogens, patients with co-infections and/or secondary infections were more likely to receive antibiotics (p < 0.001) and have elevated levels of d-dimer (p = 0.0012), interleukin-6 (p = 0.0027), and procalcitonin (p = 0.0002).The performance of conventional culture was comparable with that of mNGS in diagnosis of secondary infections. Conclusion: Co-infections and secondary infections existed in hospitalized COVID-19 patients and were relevant to the disease severity. Screening of common respiratory pathogens and hospital infection control should be strengthened.

BackgroundMycoplasma pneumoniae (M. pneumoniae) is a commonly causative pathogen for respiratory tract infections (RTIs) in humans. The epidemiological features of M. pneumoniae infections during post-epidemic, including age distribution and the seasonality of the patients, are not well investigated.MethodsWe retrospectively analyzed the clinical data of 7835 consecutive RTIs patients (3852 adults and 3983 children) who visited a teaching hospital, and defined an epidemic (2011–2013) and a post-epidemic period (2014–2016). M. pneumoniae was detected by fluorescence-quantatitive PCR in respiratory samples. Informed consent was obtained by all adults and the legal representatives of patients aged < 18 years, and the study was approved by Institutional Review Board of Beijing Chao-Yang Hospital (project approval number 10-KE-49).ResultsThe median (IQR) age was 16 (53) years (range < 0–105 years). The M. pneumoniae positive rate was 14.4% (21.2%, epidemic; 6.7%, post-epidemic), with seasonal peaks from late summer to autumn during epidemic, and from fall to winter during post-epidemic period, which was highest in children aged 7–17 years. In epidemic, no statistical difference was found in the positive rates between children and adults among most months (except February, July and August), neither for the positive rates among age groups (P = 0.801). However, in post-epidemic period, significant differences were observed in the positive rates between children and adults in nearly every month (P< 0.05 or P< 0.001, except May), as well as in the positive rates among age groups (P< 0.001). Most of the older patient admissions and all of ICU admissions occurred during the epidemic.ConclusionsDifferent patterns of age distribution and seasonality of M. pneumoniae RTIs between epidemic and post-epidemic periods were reported. Our results suggest that M. pneumoniae should be considered as a possible pathogen in pneumonia patients admitted to the ICU in the setting of an epidemic.Electronic supplementary materialThe online version of this article (10.1186/s12879-018-3250-2) contains supplementary material, which is available to authorized users.

Conditionally essential (CE) genes are required by pathogenic bacteria to establish and maintain infections. CE genes encode virulence factors, such as secretion systems and effector proteins, as well as biosynthetic enzymes that produce metabolites not found in the host environment. Due to their outsized importance in pathogenesis, CE gene products are attractive targets for the next generation of antimicrobials. However, the precise manipulation of CE gene expression in the context of infection is technically challenging, limiting our ability to understand the roles of CE genes in pathogenesis and accordingly design effective inhibitors. We previously developed a suite of CRISPR interference-based gene knockdown tools that are transferred by conjugation and stably integrate into bacterial genomes that we call Mobile-CRISPRi. Here, we show the efficacy of Mobile-CRISPRi in controlling CE gene expression in an animal infection model. We optimize Mobile-CRISPRi in Pseudomonas aeruginosa for use in a murine model of pneumonia by tuning the expression of CRISPRi components to avoid nonspecific toxicity. As a proof of principle, we demonstrate that knock down of a CE gene encoding the type III secretion system (T3SS) activator ExsA blocks effector protein secretion in culture and attenuates virulence in mice. We anticipate that Mobile-CRISPRi will be a valuable tool to probe the function of CE genes across many bacterial species and pathogenesis models. IMPORTANCE Antibiotic resistance is a growing threat to global health. To optimize the use of our existing antibiotics and identify new targets for future inhibitors, understanding the fundamental drivers of bacterial growth in the context of the host immune response is paramount. Historically, these genetic drivers have been difficult to manipulate precisely, as they are requisite for pathogen survival. Here, we provide the first application of Mobile-CRISPRi to study conditionally essential virulence genes in mouse models of lung infection through partial gene perturbation. We envision the use of Mobile-CRISPRi in future pathogenesis models and antibiotic target discovery efforts.