The enteric pathogen Campylobacter jejuni is a highly prevalent yet fastidious bacterium. Biofilms and surface polysaccharides participate in stress survival, transmission, and virulence in C. jejuni; thus, the identification and characterization of novel genes involved in each process have important implications for pathogenesis. We found that C. jejuni reacts with calcofluor white (CFW), indicating the presence of surface polysaccharides harboring ␤1-3 and/or ␤1-4 linkages. CFW reactivity increased with extended growth, under 42°C anaerobic conditions, and in a ⌬spoT mutant defective for the stringent response (SR). Conversely, two newly isolated dim mutants exhibited diminished CFW reactivity as well as growth and serum sensitivity differences from the wild type. Genetic, biochemical, and nuclear magnetic resonance analyses suggested that differences in CFW reactivity between wild-type and ⌬spoT and dim mutant strains were independent of well-characterized lipooligosaccharides, capsular polysaccharides, and N-linked polysaccharides. Targeted deletion of carB downstream of the dim13 mutation also resulted in CFW hyporeactivity, implicating a possible role for carbamoylphosphate synthase in the biosynthesis of this polysaccharide. Correlations between biofilm formation and production of the CFW-reactive polymer were demonstrated by crystal violet staining, scanning electron microscopy, and confocal microscopy, with the C. jejuni ⌬spoT mutant being the first SR mutant in any bacterial species identified as up-regulating biofilms. Together, these results provide new insight into genes and processes important for biofilm formation and polysaccharide production in C. jejuni.

Background SARS-CoV-2 antibody testing is required for estimating population seroprevalence and vaccine response studies. It may also increase case identification when as an adjunct to routine molecular testing. We performed a validation study and evaluated the use of automated high-throughput assays in a field study of COVID-19-affected care facilities. Methods Six automated assays were assessed: 1) DiaSorin LIAISON TM SARS-CoV-2 S1/S2 IgG; 2) Abbott ARCHITECT TM SARS-CoV-2 IgG; 3) Ortho VITROS TM Anti-SARS-CoV-2 Total; 4) VITROS TM Anti-SARS-CoV-2 IgG; 5) Siemens SARS-CoV-2 Total Assay; and 6) Roche Elecsys TM Anti-SARS-CoV-2. The validation study included 107 samples (42 known positive; 65 presumed negative). The field study included 296 samples (92 PCR positive; 204 PCR negative or not PCR tested). All samples were tested by the six assays. Results; All assays had sensitivities >90% in the field study, while in the validation study, 5/6 assays were >90% sensitive and DiaSorin was 79% sensitive. Specificities and negative predictive values were >95% for all assays. Field study estimated positive predictive values at 1%-10% disease prevalence were 100% for Siemens, Abbott and Roche, while DiaSorin and Ortho assays had lower PPVs at 1% prevalence, but PPVs increased at 5%-10% prevalence. In the field study, addition of serology increased diagnoses by 16% compared to PCR testing alone. Conclusions All assays evaluated in this study demonstrated high sensitivity and specificity for samples collected at least 14 days post-symptom onset, while sensitivity was variable 0-14 days after infection. The addition of serology to the outbreak investigations increased case detection by 16%.

The diagnostic sensitivity of observed and unobserved self-collected saline gargle (SG) samples for the molecular detection of SARS-CoV-2 in adults and school-aged children was evaluated against a reference standard of health care worker (HCW) collected nasopharyngeal (NP) flocked swab. A total of 46 participants had a positive NP swab sample; of these, 10 were in the observed phase and 36 were in the unobserved phase. Only one matching saline gargle sample tested negative and this was in the unobserved phase, giving an overall sensitivity of 98%. Average viral target Ct values were higher in the saline gargle samples. RNaseP Ct values were lower in unobserved collected samples compared to observed collected samples. Unobserved self-collection of SG samples is a promising outpatient testing method for COVID-19 diagnosis. The self-collection method has potential to simplify the diagnostic cycle and facilitate implementation of COVID-19 testing, particularly in settings with limited access to HCWs.

BackgroundAs part of the public health outbreak investigations, serological surveys were carried out following two COVID-19 outbreaks in April 2020 and October 2020 in one long term care facility (LTCF) in British Columbia, Canada. This study describes the serostatus of the LTCF residents and monitors changes in their humoral response to SARS-CoV-2 and other human coronaviruses (HCoV) over seven months.MethodsA total of 132 serum samples were collected from all 106 consenting residents (aged 54-102) post-first outbreak (N=87) and post-second outbreak (N=45) in one LTCF; 26/106 participants provided their serum following both COVID-19 outbreaks, permitting longitudinal comparisons between surveys. Health-Canada approved commercial serologic tests and a pan-coronavirus multiplexed immunoassay were used to evaluate antibody levels against the spike protein, nucleocapsid, and receptor binding domain (RBD) of SARS-CoV-2, as well as the spike proteins of HCoV-229E, HCoV-HKU1, HCoV-NL63, and HCoV-OC43. Statistical analyses were performed to describe the humoral response to SARS-CoV-2 among residents longitudinally.FindingsSurvey findings demonstrated that among the 26 individuals that participated in both surveys, all 10 individuals seropositive after the first outbreak continued to be seropositive following the second outbreak, with no reinfections identified among them. SARS-CoV-2 attack rate in the second outbreak was lower (28.6%) than in the first outbreak (40.2%), though not statistically significant (P>0.05). Gradual waning of anti-nucleocapsid antibodies to SARS-CoV-2 was observed on commercial (median Δ=-3.7, P=0.0098) and multiplexed immunoassay (median Δ=-169579, P=0.014) platforms; however, anti-spike and anti-receptor binding domain (RBD) antibodies did not exhibit a statistically significant decline over 7 months. Elevated antibody levels for beta-HCoVs OC43 (P<0.0001) and HKU1 (P=0.0027) were observed among individuals seropositive for SARS-CoV-2 compared to seronegative individuals.ConclusionOur study utilized well-validated serological platforms to demonstrate that humoral responses to SARS-CoV-2 persisted for at least 7 months. Elevated OC43 and HKU1 antibodies among SARS-CoV-2 seropositive individuals may be attributed to cross reaction and/or boosting of humoral response.

A comparison of rapid point of care serology tests using finger prick and venous blood was done on 278 participants. In a laboratory setting, IgG sensitivity neared 100%; however, IgG sensitivity dramatically dropped (82%) in field testing. Possible factors include finger prick volume variability, hemolysis, cassette readability and operator training.

Highlights Myalgias, headaches, loss of appetite and having three or more negative nasopharyngeal swabs were significantly associated with seropositivity among individuals with a negative or no previous diagnostic test. Canadian, European and WHO's case definitions for probable/epidemiologically-linked cases were not significantly associated with seropositivity, unlike the American definition. Public health outbreak control measures should use a low symptom threshold (particularly for generalized/systemic symptoms) for case exclusion and isolation when screening staff and residents in facility outbreaks

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