scholarly journals Intrinsic and realized generation intervals in infectious-disease transmission

2015 ◽  
Vol 282 (1821) ◽  
pp. 20152026 ◽  
Author(s):  
David Champredon ◽  
Jonathan Dushoff
Keyword(s):  
Public Health ◽  
Mathematical Models ◽  
Disease Transmission ◽  
Interval Data ◽  
Contact Tracing ◽  
Reproductive Number ◽  
Infectious Disease Transmission ◽  
Generation Interval ◽  
Public Health Strategies ◽  
The Relationship

The generation interval is the interval between the time when an individual is infected by an infector and the time when this infector was infected. Its distribution underpins estimates of the reproductive number and hence informs public health strategies. Empirical generation-interval distributions are often derived from contact-tracing data. But linking observed generation intervals to the underlying generation interval required for modelling purposes is surprisingly not straightforward, and misspecifications can lead to incorrect estimates of the reproductive number, with the potential to misguide interventions to stop or slow an epidemic. Here, we clarify the theoretical framework for three conceptually different generation-interval distributions: the ‘intrinsic’ one typically used in mathematical models and the ‘forward’ and ‘backward’ ones typically observed from contact-tracing data, looking, respectively, forward or backward in time. We explain how the relationship between these distributions changes as an epidemic progresses and discuss how empirical generation-interval data can be used to correctly inform mathematical models.

scholarly journals Mask-Ematics: Modeling the Effects of Masks in COVID-19 Transmission in High-Risk Environments

Epidemiologia ◽  
2021 ◽  
Vol 2 (2) ◽  
pp. 207-226
Author(s):  
Anthony Morciglio ◽  
Bin Zhang ◽  
Gerardo Chowell ◽  
James M. Hyman ◽  
Yi Jiang
Keyword(s):  
Public Health ◽  
High Risk ◽  
Disease Transmission ◽  
Large Fraction ◽  
Critical Mass ◽  
Transmission Model ◽  
Reproductive Number ◽  
High Quality ◽  
Moderate Quality ◽  
Epidemic Size

The COVID-19 pandemic has placed an unprecedented burden on public health and strained the worldwide economy. The rapid spread of COVID-19 has been predominantly driven by aerosol transmission, and scientific research supports the use of face masks to reduce transmission. However, a systematic and quantitative understanding of how face masks reduce disease transmission is still lacking. We used epidemic data from the Diamond Princess cruise ship to calibrate a transmission model in a high-risk setting and derive the reproductive number for the model. We explain how the terms in the reproductive number reflect the contributions of the different infectious states to the spread of the infection. We used that model to compare the infection spread within a homogeneously mixed population for different types of masks, the timing of mask policy, and compliance of wearing masks. Our results suggest substantial reductions in epidemic size and mortality rate provided by at least 75% of people wearing masks (robust for different mask types). We also evaluated the timing of the mask implementation. We illustrate how ample compliance with moderate-quality masks at the start of an epidemic attained similar mortality reductions to less compliance and the use of high-quality masks after the epidemic took off. We observed that a critical mass of 84% of the population wearing masks can completely stop the spread of the disease. These results highlight the significance of a large fraction of the population needing to wear face masks to effectively reduce the spread of the epidemic. The simulations show that early implementation of mask policy using moderate-quality masks is more effective than a later implementation with high-quality masks. These findings may inform public health mask-use policies for an infectious respiratory disease outbreak (such as one of COVID-19) in high-risk settings.

scholarly journals What is Communicable? Unaccounted Injuries and “Catching” Diabetes in an Illegible Epidemic

2019 ◽  
Vol 34 (4) ◽  
Author(s):  
Amy Moran-Thomas
Keyword(s):  
Public Health ◽  
Infectious Disease ◽  
Disease Transmission ◽  
Communicable Disease ◽  
Treatment Access ◽  
Infectious Disease Transmission ◽  
The World ◽  
Historically Situated ◽  
Over Time ◽  
Non Communicable Disease

Long-accepted models of causality cast diseases into the binary of either “contagious” or “non-communicable,” typically with institutional resources focused primarily on interrupting infectious disease transmission. But in southern Belize, as in much of the world today, epidemic diabetes has become a leading cause of death and a notorious contributor to organ failure and amputated limbs. This ethnographic essay follows caregivers’ and families’ work to survive in-between public health categories, and asks what responses a bifurcated model of infectious versus non-communicable disease structures or incapacitates in practice. It proposes an alternative focus on diabetes as a “para-communicable” condition—materially transmitted as bodies and ecologies intimately shape each other over time, with unequal and compounding effects for historically situated groups of people. The article closes by querying how communicability relates to community, and why it matters to reframe narratives about contributing causalities in relation to struggles for treatment access.

scholarly journals Risk ratios for contagious outcomes

2018 ◽  
Vol 15 (138) ◽  
pp. 20170696 ◽  
Author(s):  
Olga Morozova ◽  
Ted Cohen ◽  
Forrest W. Crawford
Keyword(s):  
Small Groups ◽  
Risk Ratio ◽  
Disease Transmission ◽  
Infectious Disease Transmission ◽  
Individual Level ◽  
Susceptibility To Infection ◽  
Definition Of ◽  
The Individual ◽  
The Relationship ◽  
Risk Ratios

Epidemiologists commonly use the risk ratio to summarize the relationship between a binary covariate and outcome, even when outcomes may be dependent. Investigations of transmissible diseases in clusters—households, villages or small groups—often report risk ratios. Epidemiologists have warned that risk ratios may be misleading when outcomes are contagious, but the nature of this error is poorly understood. In this study, we assess the meaning of the risk ratio when outcomes are contagious. We provide a mathematical definition of infectious disease transmission within clusters, based on the canonical stochastic susceptible–infective model. From this characterization, we define the individual-level ratio of instantaneous infection risks as the inferential target, and evaluate the properties of the risk ratio as an approximation of this quantity. We exhibit analytically and by simulation the circumstances under which the risk ratio implies an effect whose direction is opposite that of the true effect of the covariate. In particular, the risk ratio can be greater than one even when the covariate reduces both individual-level susceptibility to infection, and transmissibility once infected. We explain these findings in the epidemiologic language of confounding and Simpson's paradox, underscoring the pitfalls of failing to account for transmission when outcomes are contagious.

Situating ‘careful surveillance’

2021 ◽  
pp. 136787792199745
Author(s):  
Mark Andrejevic ◽  
Hugh Davies ◽  
Ruth DeSouza ◽  
Larissa Hjorth ◽  
Ingrid Richardson
Keyword(s):  
Public Health ◽  
Public Space ◽  
Social Care ◽  
Cultural Practices ◽  
Contact Tracing ◽  
Social Distancing ◽  
Health Measures ◽  
Relationship Of ◽  
The Impact ◽  
The Relationship

In this article we explore preliminary findings from the study COVIDSafe and Beyond: Perceptions and Practices conducted in Australia in 2020. The study involved a survey followed by interviews, and aimed to capture the dynamic ways in which members of the Australian public perceive the impact of Covid practices – especially public health measures like the introduction of physical and social distancing, compulsory mask wearing, and contact tracing. In the rescripting of public space, different notions of formal and informal surveillance, along with different textures of mediated and social care, appeared. In this article, we explore perceptions around divergent forms of surveillance across social, technological, governmental modes, and the relationship of surveillance to care in our media and cultural practices. What does it mean to care for self and others during a pandemic? How does care get enacted in, and through, media interfaces and public interaction?

scholarly journals Defining the need for public health control of scabies in Solomon Islands

2021 ◽  
Vol 15 (2) ◽  
pp. e0009142
Author(s):  
Susanna J. Lake ◽  
Daniel Engelman ◽  
Oliver Sokana ◽  
Titus Nasi ◽  
Dickson Boara ◽  
...  
Keyword(s):  
Public Health ◽  
Solomon Islands ◽  
Population Attributable Risk ◽  
Adjusted Relative Risk ◽  
High Burden ◽  
Clinical Assessments ◽  
Western Province ◽  
Public Health Strategies ◽  
The Village ◽  
The Relationship

Pacific Island countries have a high burden of scabies and impetigo. Understanding of the epidemiology of these diseases is needed to target public health interventions such as mass drug administration (MDA). The aim of this study is to determine the prevalence of scabies and impetigo in Solomon Islands as well as the relationship between them and their distribution. We conducted a prevalence study in 20 villages in Western Province in Solomon Islands. All residents of the village were eligible to participate. Nurses conducted clinical assessments including history features and skin examination. Diagnosis of scabies was made using the 2020 International Alliance for the Control of Scabies diagnostic criteria. Assessments were completed on 5239 participants across 20 villages. Overall scabies prevalence was 15.0% (95%CI 11.8–19.1). There was considerable variation by village with a range of 3.3% to 42.6%. There was a higher prevalence of scabies in males (16.7%) than females (13.5%, adjusted relative risk 1.2, 95%CI 1.1–1.4). Children aged under two years had the highest prevalence (27%). Overall impetigo prevalence was 5.6% (95%CI 4.2–7.3), ranging from 1.4% to 19% by village. The population attributable risk of impetigo associated with scabies was 16.1% (95% CI 9.8–22.4). The prevalence of scabies in our study is comparable to previous studies in Solomon Islands, highlighting a persistent high burden of disease in the country, and the need for public health strategies for disease control.

scholarly journals Estimating the proportion of asymptomatic COVID-19 cases in an Italian region with intermediate incidence during the first pandemic wave: an observational retrospective study

2021 ◽  
Author(s):  
Domenico Martinelli ◽  
Francesca Fortunato ◽  
Sara Mazzilli ◽  
Lucia Bisceglia ◽  
Pier Luigi Lopalco ◽  
...  
Keyword(s):  
Public Health ◽  
Clinical Signs ◽  
Virus Transmission ◽  
Contact Tracing ◽  
The Public ◽  
Health Community ◽  
Important Challenge ◽  
Asymptomatic Infections ◽  
Public Health Strategies

Abstract Early in the COVID-19 pandemic, asymptomatic transmission represented an important challenge for controlling the spread of SARS-CoV-2 through the traditional public health strategies. Further understanding of the contribution of asymptomatic infections to SARS-CoV-2 transmission has been of crucial importance for pandemic control. We conducted a retrospective epidemiological study to characterize asymptomatic COVID-19 cases occurred in the Apulia region, Italy, during the first epidemic wave of COVID-19 outbreak (February 29 - July 7, 2020). We analyzed data collected in a regional platform developed to manage surveillance activities, namely investigation and follow-up of cases and contacts, contact tracing, laboratory and clinical data collection. We included all asymptomatic cases that were laboratory-confirmed during the appropriate follow-up, defined as persons infected with SARS-CoV-2 who did not develop symptoms/clinical signs of the disease. Between February 29 and July 7, 2020, a total of 4,536 cases were diagnosed with COVID-19 among 193,757 tests performed. The group of persons with asymptomatic SARS-CoV-2 infection consisted of 903 cases; the asymptomatic proportion was 19.9% (95%CI: 18.8-21.1%); this decreased with increasing age (OR: 0.89, 95%CI: 0.83-0.96; p=0.001), in individuals with underlying comorbidities (OR: 0.55, 95%CI: 0.41-0.73; p<0.001), and in males (OR: 0.69, 95%CI: 0.54-0.87; p=0.002). The median asymptomatic SARS-CoV-2 RNA positive period was 19 days (IQR: 14-31) and the cumulative proportion of persons with resolution of infection 14 days after the first positive PCR test was 74%. As the public health community is debating the question of whether asymptomatic and late spreaders could sustain virus transmission in the communities, such cases present unique opportunities to gain insight into SARS-CoV-2 adaptation to human host. This has important implications for future COVID-19 surveillance and prevention.

scholarly journals Epidemiology of COVID-19 and effect of public health interventions, Chennai, India, March - October 2020

2021 ◽  
Author(s):  
M Jagadeesan ◽  
Parasuraman Ganeshkumar ◽  
Prabhdeep Kaur ◽  
Hemalatha Masanam Sriramulu ◽  
Manikandanesan Sakthivel ◽  
...  
Keyword(s):  
Public Health ◽  
Case Fatality ◽  
Contact Tracing ◽  
Severe Illness ◽  
List Type ◽  
Rt Pcr ◽  
Case Fatality Ratio ◽  
Metropolitan City ◽  
Lessons Learnt ◽  
Public Health Strategies

AbstractObjectivesTo describe the public health strategies and their effect in controlling the COVID-19 pandemic from March to October 2020 in Chennai, India.SettingChennai, a densely populated metropolitan city in Southern India, was one of the five cities which contributed to more than half of the COVID-19 cases in India.ParticipantsWe collected the de-identified line list of all the 192,450 COVID-19 case-patients reported from 17 March to 31 October 2020 in Chennai and their contacts for the analysis. We defined a COVID-19 case-patient based on the RT-PCR positive test in one of the Government approved labs.Outcome measuresThe primary outcomes of interest were incidence of COVID-19 per million population, case fatality ratio, deaths per million and the effective reproduction number (Rt). We also analysed the indicators for surveillance, testing, contact tracing and isolation.ResultsOf the 192,450 RT-PCR confirmed COVID-19 case-patients reported in Chennai from 17 March-31 October 2020, 114,889 (60%) were males. The highest incidence was 41,064 per million population among the 61-80 years. The incidence peaked during June 2020 at 5239 per million and declined to 3,627 per million in October 2020. The city reported 3,543 deaths, with a case fatality ratio (CFR) of 1.8% and the crude death rate was 431 per million. When lockdown began, Rt was high (4.2) in March and fluctuated from April to June 2020. The Rt dropped below one by the first week of July and remained so until October 2020, even with the relaxation of restrictionsConclusionThe combination of public health strategies controlled the COVID-19 epidemic in a large, densely populated city in India. We recommend continuing the interventions to prevent resurgence, even as vaccination is being rolled out.StrengthsWe did a comprehensive analysis of COVID-19 strategies and outcome in a large, densely populated metropolitan city in India.We documented that the community-centric public health strategies were feasible and effective in controlling the COVID-19 outbreak even in a large, thickly populated cityThe lessons learnt are relevant to similar settings in low-and middle-income countries. Given the ongoing multiple waves of COVID-19 and the difficulty in controlling the transmission, our experience and lessons learnt will be valuable for policymakers and scientific advisors globallyLimitationsWe analysed the data available from the GCC database and not from the hospitals where patients with moderate to severe illness were admitted. Hence, we could not report the severity of illness among admitted patients.Second, the COVID-19 incidence might have been underestimated while testing was low during the early phase of the epidemic

Use of Masks as a Preventative Public Health Strategy to Limit the Spread of COVID-19

2021 ◽  
pp. 1-5
Author(s):  
Wally Bartfay ◽  
Wally Bartfay ◽  
Marina Ali
Keyword(s):  
Public Health ◽  
Single Layer ◽  
Global Perspective ◽  
Contact Tracing ◽  
Global Pandemic ◽  
Health Strategy ◽  
Preventative Strategy ◽  
Viral Dose ◽  
Public Health Strategies ◽  
Health Experts

SARS-CoV-2 coronavirus (COVID-19) is a respiratory infectious disease that has caused a global pandemic of unprecedented proportions. There has been a lot of discussion and debate in social media and by public health experts about the effectiveness of masks as a preventative strategy to decrease transmission of this virus. There are two modes in which mask may be beneficial: i) To serve as a physical barrier against the virus entering or leaving the oral-nasal passages of mask wearers, and ii) to decrease the risk that the person wearing the mask might pass the virus on to someone else (e.g., via coughing). The focus of this review is on the efficacy of different masks-types, and their demonstrated effectiveness in mitigating transmission from a global perspective. Our findings reveal that the use of commercially manufactured mask greatly decreases the distribution of COVID-19, whereas single layer homemade masks also provide protection by decreasing the viral dose of exposure and limit outward aerosol particle emissions. We argue that masks are a critical component in the arsenal of public health strategies to decrease transmission of viruses, including handwashing, maintaining social distancing (2 meters), limiting large gatherings of people, isolation of suspected cases, screening, and contact tracing.

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