Symptom propagation occurs when the symptom set an individual experiences is correlated with the symptom set of the individual who infected them. Symptom propagation may dramatically affect epidemiological outcomes, potentially causing clusters of severe disease. Conversely, it could result in chains of mild infection, generating widespread immunity with minimal cost to public health. Despite accumulating evidence that symptom propagation occurs for many respiratory pathogens, the underlying mechanisms are not well understood. Here, we conducted a scoping literature review for 14 respiratory pathogens to ascertain the extent of evidence for symptom propagation by two mechanisms: dose-severity relationships and route-severity relationships. We identify considerable heterogeneity between pathogens in the relative importance of the two mechanisms, highlighting the importance of pathogen-specific investigations. For almost all pathogens, including influenza and SARS-CoV-2, we found support for at least one of the two mechanisms. For some pathogens, including influenza, we found convincing evidence that both mechanisms contribute to symptom propagation. Furthermore, infectious disease models traditionally do not include symptom propagation. We summarize the present state of modelling advancements to address the methodological gap. We then investigate a simplified disease outbreak scenario, finding that under strong symptom propagation, isolating mildly infected individuals can have negative epidemiological implications.

The bioactive chemicals in cigarette smoke (CS) and e-cigarette vapor (EV) may affect pathogenic bacteria in the nasopharyngeal microflora, which may have implications on the pathophysiology of respiratory infections in cigarette smokers and e-cigarette users. In this systematic review, we seek to synthesize the research evidence supporting this hypothesis. To address the central research question, \"what is known from the published, peer-reviewed literature about the effects of cigarette smoke or e-cigarette vapor exposure on the physiology of human pathogenic bacteria?\", we screened the PubMed®, Web of ScienceTM, and ScienceDirect databases for reports examining the virulence characteristics and gene expression in human pathogenic bacteria exposed to either CS or EV. The principal conclusion from our analysis is that exposure to either CS or EV induces the virulence of respiratory pathogenic bacteria in a strain-dependent manner, which may in turn facilitate respiratory infections in cigarette smokers and e-cigarette users. In addition, we present evidence that nicotine and reactive oxygen species are the main chemicals responsible for CS/EV-mediated alterations in bacterial physiology. We note limitations that this review does not examine reports describing the alterations in host respiratory physiology or nasopharyngeal dysbiosis caused by CS/EV exposure. Future research to determine whether CS/EV-mediated augmentation of bacterial virulence indeed plays a role in human respiratory tract infections is warranted.

This rapid review aimed to identify measures available to support those in isolation or quarantine during the coronavirus disease 2019 (Covid-19) pandemic, and determine their effectiveness in improving adherence to these recommendations and or reducing transmission. The rapid review consisted of two elements, the first was a review of guidance published by national and international agencies relating to measures to support those in isolation (due to case status) or quarantine (due to close contact status) during the Covid-19 pandemic. Five categories of support measures were identified in the international guidance, they were: Psychological, addiction and safety supports, Essential supplies, Financial aid, Information provision and Enforcement. The second element was a rapid literature review of the effectiveness of measures used to support individuals in isolation or quarantine during any pandemic or epidemic setting, due to respiratory pathogens. A systematic search of published peer-reviewed articles and nonpeer-reviewed pre-prints was undertaken from 1 January 2000 to 26 January 2021. Two Australian publications met the inclusion criteria, both based on data from a survey undertaken during the 2009 H1N1 pandemic. The first reported that 55% of households were fully compliant with quarantine recommendations, and that there was increased compliance reported in households that understood what they were meant to do compared with those who reported that they did not (odds ratio [OR]: 2.27, 95% confidence interval [CI]: 1.35-3.80). The second reported that access to paid sick and or carer\'s leave did not predict compliance with quarantine recommendations (OR: 2.07, 95% CI: 0.82-5.23). Neither reported on reduction in transmission.