The incubation period refers to the time from exposure to an infectious agent until the first sign of symptoms related to disease.
The incubation period for COVID-19 is thought to be 2 to 14 days.

COVID-19 Incubation Period

The most common symptoms of COVID-19 are fever, tiredness, and dry cough. Some patients may have aches and pains, nasal congestion, runny nose, sore throat or diarrhea. These symptoms are usually mild and begin gradually. Most people (about 80%) recover from the disease without needing special treatment. 

Symptomatic COVID-19 Infection

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

Studies on the Serial Interval of COVID-19 Categorized by Continents 

- Acta Paediatrica
- American Journal of Obstetrics & Gynecology MFM
- bioRxiv (Preprint)
- Frontiers in Pediatrics
- Immunological Reviews
- JAMA
- Morbidity and Mortality Weekly Report
- New England Journal of Medicine
- The Lancet
- Mycoses



References for Symptomology of COVID-19 Categorized by Journal

- Geographic Location
- Demographic Group

Categorizations of Symptomology of COVID-19

Several studies have shown that COVID-19 can be transmitted by individuals who do not show any symptoms, or who are "asymptomatic". Because asymptomatic individuals are not routinely tested, the prevalence of asymptomatic infection is not well-defined.

Asymptomatic COVID-19 Infection

Currently, there is no FDA-approved, consistent treatment plan for COVID-19. Treatment depends on the severity of disease, the patient's ability to self-isolate, and the presence of other risk factors. Individuals with mild to moderate cases of COVID-19 are able to treat themselves at home without hospitalization or clinical care. If an individual is hospitalized, treatments will focus on managing the most common and severe COVID-19 complications. 

Therapeutic Treatment of COVID-19

key symptoms and biochemical/radiological features of clinical course of COVID-19

Clinical Course of COVID-19 (graphic)

- Gastrointestinal (GI) distress
- Sensorineural impairment
- Loss of smell and taste
- Dysregulated blood clotting
- Hepatitis
- Acute cardiac and renal injury irrespective of age and health status

Symptoms shown by individuals infected with COVID-19

Researchers have found 42.3% of people infected with COVID-19 still have symptoms after 30 days of infection, 33.8% after 60 days and 24.1% after 90 days. Infected people with more initial symptoms are more likely to have long term effects of the virus. Symptoms like anosmia, ageusia, difficulty concentrating, difficulty breathing, memory loss, confusion, headache, chest pain etc were significantly enriched in COVID-19 patients after 30 days. 

Long Term Symptoms of COVID-19

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

University of Michigan - Ann Arbor

Smith College

- Affected organs and organ systems
- Circadian Physiology in relation to COVID-19
- Exercise/Physical Activity and COVID-19
- Immune response to COVID-19
- Laboratory methods
- Pathogenesis
- Patient comorbidities 
- Symptomology 
- Genetic mechanisms in COVID-19
- The body's response to stress hormones






Focuses of Human physiology studies on COVID-19

- 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

World Health Organization

Retrospective epidemiological studies using clinical data and experimental molecular biologies studies have revealed biomarkers of COVID-19.  These elements not only reveal how COVID-19 mechanistically affects the body, but they may also be risk factors for developing severe symptoms and act as targets for pharmacological intervention.  They include:

- A1AT protection
- ACE2 expression and activity
- ADAM17 sheddase activity
- Furin protease activity
- Irregular respiratory function
- Pro-inflammatory cytokine concentration in the plasma
- TMPRSS2 serine protease genetic variation
- Variation in genetic susceptibility to SARS-CoV-2
- Viral interactions with glycosaminoglycans
- Nsp (Non-specific Protein) Activity
- Neuropilin-1 expression


Pathogenesis of COVID-19

Current studies show that many organs that are heavily affected by COVID-19 have a high expression level of ACE2.

- Cardiovascular system
- Central nervous system (CNS)
- Gastrointestinal tract (GI)
- Kidney
- Liver 
- Lungs (Respiratory System)
- Peripheral nervous system (PNS)
- Testis

Organs and Organ Systems Affected by COVID-19

- Animal models
- Cell lines
- Genetically engineered SARS-CoV-2

Laboratory Methods in COVID-19 Research

Infection by SARS-CoV-2, as is with other viral infections, induces a two-phased immune response in the human body, described in the figure below: 
- Innate (rapid, natural, non-specific) 
- Adaptive (slow, acquired, specific)

Those two branches of the immune system cooperate with one another, and can be distinguished based on the cell-types involved (immune response vs white blood cells). However, the adaptive system is further broken down by the type of mechanism:

- Cell-mediated
- Antibody-mediated

Current research around COVID-19 immunity aims at uncovering the interaction between SARS-CoV-2 and the host's immune response, with questions related to pathogenesis, severity, and intervention.

Immune Response to COVID-19 

Symptomology of COVID-19 

- Pituitary gland: improper functioning of the hypothalamus in association with pituitary gland; changes the metabolism of ADH (regulates the amount of water in the kidneys); abnormal sodium levels
- Thyroid: sick euthyroid syndrome → decrease in size of thyroid gland; changes in TSH levels
- Adrenal gland: increased chance of COVID-19 infection if presented with Cushing’s syndrome (too much cortisol) or Addison’s disease (inadequate aldosterone and cortisol)
- Pancreas: those with diabetes are at higher risk of getting COVID-19
- Bone: low vitamin D and hypocalcemia

Dysfunctions/ diseases in endocrine glands/organs that could lead to greater susceptibility to COVID-19

Exercise and physical activity induce physiological changes on many levels, the effects of which are best understood using a biopsychosocial approach.  The bidirectional relationship between exercise and Covid-19 can be further broken down into different components:
- Exercise/PA and COVID-19 by geographical location
- Exercise/PA and COVID-19 by demographics


Exercise/Physical Activity (PA) and Covid-19

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

Circadian biology refers to any biological process that has a rhythmic component dependent on time of day.  Understanding the relation between COVID-19 and circadian rhythm could help improve clinical management in treating COVID-19.

Circadian Physiology in relation to COVID-19

ARTICLES RESEARCHED
- Genetic mechanisms of critical illness in Covid-19
- Epigenetic dysregulation of ACE2 and interferon-regulated genes might suggest increased COVID-19 susceptibility and severity in lupus patients

Genetic mechanisms in COVID-19

Levels of stress may increase in those diagnosed with COVID-19, resulting in an alteration in stress hormone levels and the body's ability to cope with the stress.

The Body's Physiological Response to Stress Hormones In COVID-19 Patients

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

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

Psychological Effects of COVID-19 Pandemic

- Schools (K-12)

- Universities/Colleges

- Summer Camps

- Daycares

- Nurseries

Re-opening Childcare/ Educational Environments

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. 

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

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