The reproductive/reproduction number of COVID-19 is estimated to be between 2 and 2.5 as of March 6, 2020. 

Reproductive Number of COVID-19

- American Association for the Advancement of Science

- American Veterinary Medical Association (AVMA)

- Asian Pacific Journal of Tropical Medicine (APJTM)

- BioMed Research International

- BioRxiv (Preprint)

- Emerging Infectious Diseases

- Environmental Research 

- Forensic Science International: Reports

- Infectious Disease Modeling 

- Infectious Diseases Society of America (Clinical Infectious Disease)

- Jama Network Open

- Journal of Travel Medicine

- Nature Communications

- Risk Analysis

- Science of the Total Environment

- Social Science Research Network (SSRN)

- The International Journal of Infectious Diseases  

- The Journal of the American Medical Association (JAMA)

- The Lancet

- The Lancet Infectious Diseases 

- The New England Journal of Medicine

- Travel Medicine and Infectious Diseases

- Veterinary Quarterly

- Virology Journal 

- World Journal of Clinical Cases




Transmission of COVID-19 References by journal

Cluster transmission has been noted in many COVID-19 studies
It is characterized by infections that are concentrated within a given area, often within families or social circles 

Cluster Transmission of COVID-19

- Asia
- Africa 
- North America
- South America
- Antarctica
- Europe
- Australia

Classification of studies on COVID-19 Transmission by Continents

Indirect Transmission of COVID-19

Previous reports indicate that asymptomatic transmission is possible, but since they’re hard to track, this poses a significant challenge to infection control practices.

Implications of Asymptomatic COVID-19 Transmission

- Super spreading events

- Climate

- Season

- Location

- UV & sunlight on the virus

- Virus concentrations in wastewater 

Factors that affect the transmission of COVID-19

Live animal food markets carry a great risk of transmitting zoonotic diseases compounded by the lack of safe and regulated hygienic practices. The Huanan South Seafood Market in Wuhan, China which sells wild exotic and domesticated live animals for consumption, was identified to be the epicenter of the COVID-19 pandemic. Bats are implicated to be the reservoir hosts of the virus, as SARS-CoV-2 is 96% genetically identical to bat coronavirus. Pangolins are also a possible host, as the RBD in the S protein show similarity to Pangolin-CoV. 

Any infections in animals with COVID-19 should be reported to the World Organization for Animal Health (OIE). The CDC reports that a number of pets worldwide are confirmed positive for COVID-19, though the risk of animal-human transmission in these cases are yet unclear.

Zoonotic Transmission of COVID-19

In a comprehensive case study, Vivanti et al. report the first transplacental transmission of SARS-CoV-2 with clinical manifestation in the newborn, consistent with neurological signs and symptoms of the virus. 

Transplacental Transmission of COVID-19

Determining this has critical implications: 

If primarily spread via droplets, then masks, distancing rule (6ft), etc. are effective in preventing transmission. Conversely, if primarily spread via aerosols, then preventative measures become less effective and thus need to be modified. 

Examining the source of transmission for both types of respiratory particles are crucial.



Aerosol versus Droplet Debate

Transmission of COVID-19 references by organization

Current data shows that infection rates of SARS-CoV-2 are low among children. It then can be said that they do not play a prominent role in the disease transmission of COVID-19 during the pandemic. Although the actual infection rate cannot be known due to under-reporting and a lack of available results from seroepidemiological studies, there are numerous findings against an increased risk of infection from children and findings that show a lower rate of infection and of contagion especially in children under the age of 10. It was also found that the transmission of SARS-CoV-2 is typically from an infected adult to a child and that a lack of evidence remains for the transmission of infection from an infected child to an adult. The cause of this lower virus transmission rate is still unknown, which calls for further investigations. 

Role of Children In Transmission

- Genomic Evidence of In-Flight Transmission of SARS-CoV-2 Despite Predeparture Testing
-  In-flight transmission of SARS-CoV-2: a review of the attack rates and available data on the efficacy of face masks

Air travel and COVID-19 transmission 

SARS-CoV-2 is a branch of the SARS-Cov family. It is spherical and enveloped with club-shaped spikes on the surface. Thus, it has the shape of a solar corona. Inside the nucleoplasm, the virus has single-strand RNA, which stores the genetic information of this virus. Due to the property of protein and RNA, the SARS-CoV-2 should be sensitive to temperature.

How Temperature Affects the Transmission of COVID-19

COVID-19 is spread through person-to-person transmission. The virus spreads mainly through close personal contact (such as when people are within 6 feet of one another) and through the respiratory droplets of someone infected with COVID-19.  Aerosol transmission is also likely, but the relative contribution of these smaller respiratory particles is not completely understood. While less common, spreading can also occur when people touch contaminated objects or surfaces and then their faces, eyes, or mouth. 

University of Michigan - Ann Arbor

University of California, Davis

Syracuse University

- Case Demographics of Patients
- Categorized by Geographic Location
- Communicable Period
- Control Strategies
- Disparate COVID-19 Outcomes
- Fatality
- Interventions
- Patient Comorbidities
- Patient Laboratory Results
- Psychological effects
- Recovery & Rehabilitation
- Re-opening of Childcare/ Educational Environments
- Secondary Infections
- Signs
- Symptomology
- Time from Onset to Reporting
- Telehealth (telemedicine)
- Transmission
- Risk Factors
- COVID-19 Vaccination Uptake

Focuses of Epidemiological studies on COVID-19

Centers for Disease Control and Prevention. (n.d.). Centers for Disease control and Prevention. Centers for Disease Control and Prevention. https://www.cdc.gov/. 

Centers for Disease Control and Prevention

World Health Organization

Due to differences in testing and case definitions, as well as how new COVID-19 is, the fatality of the virus is not well-defined yet.

Fatality of COVID-19

Countries have implemented multiple control strategies for reducing the spread of COVID-19, such as closing schools and businesses to enforce social distancing.

Struggle pertaining to controlling the virus:
The epidemiology of the respiratory virus changes rapidly. Reponses have to be nimble. Given that everyone is susceptible to for which we lack effective biologic interventions, the response has required large-scale behavior change, including social distancing and public masking.

Control Strategies for COVID-19

- Age
- Education
- Employment
- Ethnicity
- Gender
- Income
- Marital status
- Race





Case Demographics of Patients with COVID-19

- Asia
- Africa 
- North America
- South America
- Europe
- Australia & Oceania 

Epidemiological studies on COVID-19 Categorized by Continents

The progression of COVID-19 varies greatly by individual and demographic, as do many of the factors related to the disease. Studies have been analyzing the disease progression timeline, or the time frames before patients feel symptoms, are admitted to the hospital, are admitted to the ICU, are put on a mechanical ventilator, experience acute respiratory distress syndrome, etc. Not every COVID-19 case will reach each of these events.

COVID-19 Clinical Disease Progression Timeline

- 0-19 (n=123): 0%
- 20-44 (n=705): 0.1–0.2%
- 45-54 (n=429): 0.5–0.8%
- 55-64 (n=429): 1.4–2.6%
- 65-74 (n=409): 2.7–4.9%
- 75-84 (n=210): 4.3–10.5%
- greater than or equal to 85 (n=144): 10.4–27.3%
- Total (n=2,449): 1.8–3.4%

Case-Fatality Among COVID-19 Patients in the United States by Age

Following a primary infection of SARS-CoV-2, some patients acquire a secondary infection of SARS-CoV-2, or a co-infection with a different bacteria or virus

Secondary/Co-Infections of COVID-19

COVID-19 patients have gone through laboratory testing to determine the impact and extent of SARS-CoV-2 on the body.

COVID-19 Laboratory Results

The spread of the SARS-CoV-2 virus has produced or highlighted disparate outcomes of different types between population groups all over the world. Health disparities can highlight inequitable access, treatment, etc. within a country or state and often indicate the need for public health intervention.

Disparate COVID-19 Outcomes

Due to the varying experiences for those with COVID-19, recovery and rehabilitation look different for many individuals. As a baseline, "for persons recovered from COVID-19 illness, CDC recommends that isolation be maintained for at least 10 days after illness onset and at least 3 days (72 hours) after recovery. Illness onset is defined as the date symptoms begin. Recovery is defined as resolution of fever without the use of fever-reducing medications with progressive improvement or resolution of other symptoms. Ideally, isolation should be maintained for this full period to the extent that it is practicable under rapidly changing circumstances."

COVID-19 Recovery & Rehabilitation

- Resuscitation
- Convalescent Plasma (CP) Transfusion

COVID-19 Patient Interventions

The seroprevalence of COVID-19 is the measurement of the level of the pathogen in a population. There have been difficulties with estimating the seroprevalence in large populations because of the unknown qualities of COVID-19, expense in widespread population collection, asymptomatic infection, etc.

Seroprevalence of SARS-CoV-2 (COVID-19) 

A communicable period is defined as the interval from the first day of positive ribonucleic acid test to the first day of continuous negative test. For COVID-19, the communicable period has been established as two days before onset of symptoms until three days of symptom relief and no fever. 

Communicable Period of COVID-19

- Fever (when high temperature is measured)
- Laboratory confirmation of illness via viral testing
- Radiological lung abnormalities such as ground-glass chest and stripe shadowing


Clinical Characteristics of Asymptomatic COVID-19 Patients

Telehealth are health-related services and information through electronic communication technologies to help patients with or people influenced by COVID-19. It allows long-distance patient and clinician care, education, and monitoring. Telemedicine is sometimes used as a synonym, or is used in a more limited sense to describe remote clinical services, such as diagnosis and monitoring. 

Telehealth (telemedicine) and COVID-19

Presence and severity of symptoms of COVID-19 depend largely on individual characteristics. COVID-19 produces both symptomatic and asymptomatic infection.

Symptomology of COVID-19 

The psychological effect COVID-19 is having on the populations affected by the pandemic

Psychological Effects of COVID-19 Pandemic

COVID-19 comorbidities are high risk conditions that put patients at greater risk for infection and negative outcomes. Some COVID-19 comorbidities have been found to be: 
- Cancer 
- Cardiovascular Disease
- Diabetes
- Digestive Diseases
- HIV
- Hypertension
- Immunological Disease
- Liver Injury
- Obesity
- Renal disease
- Respiratory System Disease

COVID-19 Patient Comorbidities

- Schools (K-12)

- Universities/Colleges

- Summer Camps

- Daycares

- Nurseries

Re-opening Childcare/ Educational Environments

Transmission of COVID-19

- smoking
- high BMI
- old age
- congregate housing
- environmental conditions
- Immune system conditions

Risk Factors For COVID-19

We can explore factors that affect the uptake of established adult vaccinations to inform efforts of COVID-19 vaccine acceptance. 

- Social Factors 
- Knowledge, Attitudes, and Beliefs
- Racial Factors
- Age

Learn Before

Related

Learn After