The global dissemination of ceftriaxone-resistant Neisseria gonorrhoeae FC428-like strains poses a public health concern. To assess and follow their spread, establishing effective antimicrobial resistance (AMR) surveillance systems is essential.

This study aimed to track ceftriaxone-resistant FC428-like strains in parts of China, using a molecular screening tool.

Samples were collected from Sichuan, Zhejiang, Shanghai, and Guangdong provinces between 2019 and 2021. We employed a rapid molecular tool − the high-resolution melting analysis-based FC428 (HRM-FC428) assay, to screen for FC428-like strains. All FC428-like strains detected were further characterised by genotyping and PCR-sequencing.

Of 1,042 tested samples, 44 harboured the penA-60.001 allele linked to ceftriaxone resistance, revealing a 4.2% prevalence of FC428-like strains. The HRM-FC428 assay additionally uncovered six strains with mosaic penA-195.001 or penA-232.001 alleles, both bearing the A311V mutation, a ceftriaxone resistance marker. During the study, the prevalence of FC428-like strains among overall samples appeared to increase, with rates of 2.8% (11/395) in 2019, 4.2% (16/378) in 2020, and 6.3% (17/269) in 2021. Some strains’ sequence types (ST)s were identified across provinces (e.g. ST1903, ST1600) and most strains (24/44) were ST1903, an ST also reported in other regions/countries, suggesting local evolution and global transmission.

Our work underscores the value of culture-independent antimicrobial resistance monitoring and validates the use of molecular diagnostic tools, like the HRM-FC428 assay for this purpose. This study offers insights into the complex landscape of ceftriaxone-resistant N. gonorrhoeae, emphasising the importance of continued surveillance and global collaboration to mitigate this growing public health threat.

Infectiousness of respiratory viral infections is quantified as plaque forming units (PFU), requiring resource-intensive viral culture that is not routinely performed. We hypothesised that RNA viral load (VL) decline time (e-folding time) in people might serve as an alternative marker of infectiousness.

This study’s objective was to evaluate the association of RNA VL decline time with RNA and PFU VL area under the curve (AUC) and transmission risk for SARS-CoV-2 and influenza A virus.

In SARS-CoV-2 and influenza A virus community cohorts, viral RNA was quantified by reverse transcription quantitative PCR in serial upper respiratory tract (URT)-samples collected within households after an initial household-member tested positive for one virus. We evaluated correlations between RNA VL decline time and RNA and PFU-VL AUC. Associations between VL decline time and transmission risk in index-contact pairs were assessed.

In SARS-CoV-2 cases, we observed positive correlations between RNA VL decline time and RNA and PFU VL AUC with posterior probabilities 1 and 0.96 respectively. In influenza A cases a positive correlation between RNA VL decline time and RNA VL AUC was observed, with posterior probability of 0.87. Index case VL decline times one standard deviation above the cohort-mean showed a relative increase in secondary attack rates of 39% (95% credible interval (CrI): −6.9 to 95%) for SARS-CoV-2 and 25% (95% CrI: −11 to 71%) for influenza A virus.

We identify VL decline time as a potential marker of infectiousness and transmission risk for SARS-CoV-2 and influenza A virus. Early ascertainment of VL kinetics as part of surveillance of new viruses or variants could inform public health decision making.