Background The ongoing coronavirus disease 2019 (COVID-19) pandemic has resulted in implementation of public health measures worldwide to mitigate disease spread, including; travel restrictions, lockdowns, messaging on handwashing, use of face coverings and physical distancing. As the pandemic progresses, exceptional decreases in seasonal respiratory viruses are increasingly reported. We aimed to evaluate the impact of the pandemic on laboratory confirmed detection of seasonal non-SARS-CoV-2 respiratory viruses in Canada. Methods Epidemiologic data were obtained from the Canadian Respiratory Virus Detection Surveillance System. Weekly data from the week ending 30 th August 2014 until the week ending the 13 th March 2021 were analysed. We compared trends in laboratory detection and test volumes during the 2020/2021 season with pre-pandemic seasons from 2014 to 2019. Findings We observed a dramatically lower percentage of tests positive for all seasonal respiratory viruses during 2020-2021 compared to pre-pandemic seasons. For influenza A and B the percent positive decreased to 0•0015 and 0•0028 times that of pre-pandemic levels respectively and for RSV, the percent positive dropped to 0•0169 times that of pre-pandemic levels. Ongoing detection of enterovirus/rhinovirus occurred, with regional variation in the epidemic patterns and intensity. Interpretation We report an effective absence of the annual seasonal epidemic of most seasonal respiratory viruses in 2020/2021. This dramatic decrease is likely related to implementation of multi-layered public health measures during the pandemic. The impact of such measures may have relevance for public health practice in mitigating seasonal respiratory virus epidemics and for informing responses to future respiratory virus pandemics. Funding No additional funding source was required for this study.

The biocide chlorhexidine (CHX) as well as additional membrane-active agents were shown to induce expression of the mexCD-oprJ multidrug efflux operon, dependent upon the AlgU stress response sigma factor. Hyperexpression of this efflux system in nfxB mutants was also substantially AlgU dependent. CHX resistance correlated with efflux gene expression in various mutants, consistent with MexCD-OprJ being a determinant of CHX resistance.Pseudomonas aeruginosa is an opportunistic human pathogen characterized by an innate resistance to multiple antimicrobials (13), resistance increasingly attributable to the operation of broadly specific, tripartite multidrug efflux systems of the resistance-nodulation-division (RND) family (35,36). One of these, MexCD-OprJ, was originally identified as a determinant of fluoroquinolone resistance (17) but is known to accommodate a variety of clinically relevant antimicrobials (35, 36) as well as biocides (5), dyes, detergents, and organic solvents (27,45,46). MexCD-OprJ is typically quiescent in wild-type cells (20,46), with expression following mutation of the nfxB gene (16,22,23,50) that is divergently transcribed from the mexCDoprJ operon and encodes a repressor of mexCD-oprJ expression (37). Little is known about the signal(s) to which this regulator responds in naturally promoting efflux gene expression, although mexCD-oprJ is inducible by the biocides benzalkonium chloride and chlorhexidine (CHX) (33). These biocides are known to interact with and disrupt bacterial membranes (8), with the possibility that mexCD-oprJ expression is a response to membrane damage/envelope stress. Envelope stress responses (ESRs) are well documented in bacteria (40, 41), with the extracytoplasmic sigma factor RpoE being a key regulator of ESRs in Escherichia coli and other gram-negative bacteria (1,40,41). The RpoE homologue in P. aeruginosa is AlgU, first identified as a regulator of alginate production in mucoid isolates recovered from the lungs of cystic fibrosis patients (15, 28) and shown to be functionally interchangeable with RpoE (51). This study was undertaken to assess the contribution of MexCD-OprJ to biocide resistance in P. aeruginosa and its possible regulation as part of an ESR.Bacterial strains and plasmids used in this study are listed in Table 1. Bacteria were cultivated at 37°C in Luria broth (LB) (34) supplemented with antibiotics to maintain plasmids as needed (for pEX18Tc and derivatives, tetracycline was used [10 g/ml for E. coli and 50 to 100 g/ml for P. aeruginosa]; for pMMB206 and derivatives, chloramphenicol was used [10 g/ml for E. coli and 150 g/ml for P. aeruginosa]; for pK18MobSacB and derivatives, kanamycin was used [50 g/ml for E. coli and 750 to 1,500 g/ml for P. aeruginosa as indicated]; for miniCTX-lacZ and derivatives, tetracycline was used [10 g/ml for E. coli and 25 g/ml for P. aeruginosa]; and for pUC19 and derivatives, ampicillin was used [100 g/ml for E. coli]). AlgU-encoding plasmid pSF02 was constructed by amplifying the algU gene from the chromosome (isol...

The distribution of upper respiratory viral loads (VL) in asymptomatic children infected with SARS-CoV-2 is unknown. We assessed PCR cycle threshold (Ct) values and estimated VL in infected asymptomatic children diagnosed in nine pediatric hospital testing programs. Records for asymptomatic and symptomatic patients with positive clinical SARS-CoV-2 tests were reviewed. Ct values were adjusted by centering each value around the institutional median Ct value from symptomatic children tested with that assay, and converted to estimated VL (copies/mL) using internal or manufacturer data. Adjusted Ct values and estimated VL for asymptomatic versus symptomatic children (118 vs. 197 ages 0-4; 79 vs 97 ages 5-9; 69 vs 75 ages 10-13; 73 vs 109 ages 14-17) were compared. The median adjusted Ct value in asymptomatic children was 10.3 cycles higher than for symptomatic children (p< 0.0001), and VL 3-4 logs lower (p<0.0001); differences were consistent (p<0.0001) across all four age brackets. These differences were consistent across all institutions and by sex, ethnicity, and race. Asymptomatic children with diabetes (OR 6.5, p = 0.01), recent contact (OR 2.3, p = 0.02), and testing for surveillance (OR 2.7, p = 0.005) had higher estimated risk of having a Ct value in the lowest quartile than children without, while immunocompromise had no effect. Children with asymptomatic SARS-CoV-2 infection had lower levels of virus in the nasopharynx/oropharynx than symptomatic children, but timing of infection relative to diagnosis likely impacted levels in asymptomatic children. Caution is recommended when choosing diagnostic tests for screening of asymptomatic children.

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