Background: Coinfection with influenza virus and bacteria is a major cause of high mortality during flu pandemics. Understanding the mechanisms behind such coinfections is of utmost importance both for the clinical treatment of influenza and the prevention and control of epidemics.Methods: To investigate the cause of high mortality during flu pandemics, we performed coinfection experiments with H1N1 influenza virus and Staphylococcus aureus in which mice were infected with bacteria at time points ranging from 0 to 7 days after infection with influenza virus.Results: The mortality rates of mice infected with bacteria were highest 0–3 days after infection with influenza virus; lung tissues extracted from these co-infected mice showed higher infiltrating cells and thicker lung parenchyma than lung samples from coinfected mice in which influenza virus was introduced at other times and sequences. The levels of interferon (IFN)-γ, tumor necrosis factor (TNF)-α, interleukin (IL)-8, and IL-6 in the 0–3 day coinfected group were significantly higher than those in the other groups (p < 0.01), as were the mRNA levels of IFN-γ, IL-6, and TNF-α. Coinfection with influenza virus and S. aureus led to high mortality rates that are directly dependent on the sequence and timing of infection by both pathogens. Moreover, coinfection following this particular schedule induced severe pneumonia, leading to increased mortality.Conclusions: Our data suggest that prevention of bacterial co-infection in the early stage of influenza virus infection is critical to reducing the risk of clinical mortality.

To rapidly identify individuals infected with severe acute respiratory syndrome coronavirus‐2 (SARS‐CoV‐2) and control the spread of coronavirus disease (COVID‐19), there is an urgent need for highly sensitive on‐site virus detection methods. A clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR‐associated protein (Cas)‐based molecular diagnostic method was developed for this purpose. Here, a CRISPR system‐mediated lateral flow assay (LFA) for SARS‐CoV‐2 was established based on multienzyme isothermal rapid amplification, CRISPR‐Cas13a nuclease, and LFA. To improve the limit of detection (LoD), the crispr RNA, amplification primer, and probe were screened, in addition to concentrations of various components in the reaction system. The LoD of CRISPR detection was improved to 0.25 copy/μl in both fluorescence‐ and immunochromatography‐based assays. To enhance the quality control of the CRISPR‐based LFA method, glyceraldehyde‐3‐phosphate dehydrogenase was detected as a reference using a triple‐line strip design in a lateral flow strip. In total, 52 COVID‐19‐positive and 101 COVID‐19‐negative clinical samples examined by reverse transcription polymerase chain reaction (RT‐PCR) were tested using the CRISPR immunochromatographic detection technique. Results revealed 100% consistency, indicating the comparable effectiveness of our method to that of RT‐PCR. In conclusion, this approach significantly improves the sensitivity and reliability of CRISPR‐mediated LFA and provides a crucial tool for on‐site detection of SARS‐CoV‐2.

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In 2007, an outbreak of foodborne botulism occurred in Hebei province, China. An epidemiological investigation and laboratory detection studies showed that sausage contaminated by type A Clostridium botulinum caused this outbreak of food poisoning. Its clinical and epidemiological features were different from previous reports of food poisoning.

Intra-host evolution of SARS-CoV-2 has not been reported among asymptomatic cases, though this phenomenon was observed in a few symptomatic and immunocompromised cases. Here, we identified six asymptomatic cases who were persistently positive for SARS-CoV-2 RNA up to 120 days. Phylogenetic analysis of 40 serial whole-genome sequences from the six cases revealed dynamic mutations of the virus. To explore the possible mechanism contributing to the persistent infection, we investigated immune responses. The six cases had comparable specific antibodies with other 24 non-persistent asymptomatic cases, but they had significantly lower antibody levels than symptomatic cases. Although the virus-specific memory B and T cells were detected in the three groups of cases, the six cases showed an upregulation of CD4 regulatory T cells, which was negatively correlated with low levels of activated CD4 + and CD8 + T cells. These findings imply that dysregulation of immune responses might contribute to persistent infection.