Causes and Transmission
COVID-19 is caused by infection with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The virus spreads primarily through respiratory droplets and smaller aerosols released when an infected person coughs, sneezes, speaks, sings, or breathes. These particles can be inhaled by others or land on mucous membranes in the eyes, nose, or mouth. Infection occurs when the virus binds to receptors on human cells, entering and replicating to cause illness. While transmission is most common in close proximity, the virus can accumulate in poorly ventilated indoor spaces.

Risk Factors
Certain factors increase the likelihood of developing severe illness if infected. Age is a significant predictor, with risk increasing substantially for adults over the age of 50 and especially those over 65. Underlying medical conditions also play a major role in disease severity. Common risk factors include:

• Chronic lung diseases such as COPD, asthma, or interstitial lung disease
• Heart conditions, including heart failure and coronary artery disease
• Immunocompromised states due to cancer treatment, organ transplants, or HIV
• Metabolic conditions such as diabetes and obesity
• Pregnancy and recent pregnancy

Prevention Strategies
Preventive measures focus on reducing the risk of infection and minimizing the severity of disease if infection occurs. Vaccination is the primary tool for preventing severe outcomes, hospitalization, and death. To reduce the spread of the virus, health authorities recommend a combination of strategies depending on local transmission levels:

• Wearing high-quality masks (such as N95 or KN95) in crowded indoor settings
• Improving ventilation and air filtration in indoor spaces
• Practicing good hand hygiene by washing hands frequently with soap and water
• Staying home and testing when symptoms develop to prevent infecting others

Common Signs and Symptoms
Symptoms of COVID-19 can appear 2 to 14 days after exposure to the virus. The presentation varies widely, ranging from no symptoms (asymptomatic) to severe disease. Symptoms may change as new variants of the virus emerge. Frequently reported symptoms include:

• Fever or chills
• Cough
• Shortness of breath or difficulty breathing
• Fatigue
• Muscle or body aches
• Headache
• New loss of taste or smell
• Sore throat
• Congestion or runny nose
• Nausea, vomiting, or diarrhea

Diagnostic Tests
Clinicians and individuals identify COVID-19 using viral tests that detect the current presence of the virus. There are two primary types of diagnostic tests:

• Nucleic Acid Amplification Tests (NAATs): These tests, such as PCR tests, detect the genetic material of the virus. They are generally more sensitive and are often performed in a laboratory or clinic, though some rapid molecular tests exist.
• Antigen Tests: These are rapid tests that detect specific proteins on the surface of the virus. They are widely available for home use and produce results in 15 to 30 minutes. While convenient, they may be less sensitive than PCR tests, sometimes requiring repeat testing if the initial result is negative but symptoms persist.

Differential Diagnosis
Because the symptoms of COVID-19 are non-specific, it is often confused with other respiratory infections. Clinicians may need to distinguish it from:

• Seasonal influenza (the flu)
• Respiratory Syncytial Virus (RSV)
• The common cold (rhinovirus)
• Allergic rhinitis (hay fever)
• Streptococcal pharyngitis (strep throat)

Home Management and Self-Care
Most cases of COVID-19 are mild to moderate and can be managed at home. The goal of self-care is to relieve symptoms and prevent dehydration while the immune system fights the virus. Recommended strategies include:

• Getting plenty of rest to support immune function
• Drinking fluids like water, broth, or electrolyte solutions to stay hydrated
• Using over-the-counter fever reducers and pain relievers (such as acetaminophen or ibuprofen) to manage fever and body aches
• Monitoring oxygen levels with a pulse oximeter if advised by a healthcare provider

Medical Treatments
For individuals at high risk of severe illness, specific prescription treatments are available. These medications are most effective when started within a few days of symptom onset. Options may include:

• Antiviral medications taken orally (such as nirmatrelvir with ritonavir) to stop the virus from replicating
• Intravenous antiviral therapy (such as remdesivir) for patients who cannot take oral medications or require hospitalization
• Corticosteroids (such as dexamethasone) and immunomodulators for hospitalized patients requiring oxygen, to reduce dangerous inflammation

When to Seek Medical Care
While most people recover at home, it is vital to recognize when the condition is worsening. Emergency medical care should be sought immediately if any of the following warning signs appear:

• Trouble breathing
• Persistent pain or pressure in the chest
• New confusion
• Inability to wake or stay awake
• Pale, gray, or blue-colored skin, lips, or nail beds, depending on skin tone

Disease Severity and Course
COVID-19 ranges from asymptomatic or mild respiratory symptoms to critical illness involving respiratory failure, septic shock, or multiple organ dysfunction. In mild cases, recovery typically occurs within one to two weeks. Severe cases may require hospitalization, supplemental oxygen, or mechanical ventilation and can take weeks or months for recovery. The disease course often begins with viral replication symptoms (fever, cough) and may progress to an inflammatory phase in the second week, which is often when respiratory status worsens in severe cases.

Prognosis and Complications
The overall prognosis for the majority of people is good, especially for those who are up to date on vaccinations and have access to antiviral treatments. However, the virus can lead to serious complications, including:

• Pneumonia and Acute Respiratory Distress Syndrome (ARDS)
• Blood clots in the lungs, legs, or other areas
• Kidney injury or failure
• Cardiac complications such as myocarditis (inflammation of the heart muscle)

Long-Term Effects (Long COVID)
Some individuals experience symptoms that last for weeks, months, or even years after the acute infection has cleared. This condition, known as Long COVID or Post-COVID Conditions, can affect anyone, including those who had mild initial illness. Symptoms are diverse and can include severe fatigue, post-exertional malaise, cognitive impairment (brain fog), heart palpitations, and shortness of breath.

Impact on Daily Activities
An active COVID-19 infection requires isolation to prevent spreading the virus to others, which disrupts work, school, and social obligations. The physical symptoms, such as extreme fatigue and brain fog, can make completing basic daily tasks difficult. Even after the contagious period ends, lingering symptoms may affect stamina and concentration. The mental and emotional toll of isolation, fear of long-term health effects, and disruption of routine can also cause anxiety or depression. Coping strategies include pacing activities to conserve energy, maintaining social connections virtually, and seeking accommodations at work or school during recovery.

Questions to Ask Your Healthcare Provider
Preparing a list of questions can help patients navigate their diagnosis and recovery. Consider asking:

• Am I eligible for antiviral treatments based on my health history?
• What specific symptoms indicate that I need to go to the hospital?
• How long do I need to isolate from my family members?
• When is it safe for me to return to work or exercise?
• What signs of Long COVID should I watch for in the coming weeks?
• Are there specific over-the-counter medications I should avoid?

Q: Is COVID-19 just like the flu?
A: While both are respiratory viruses with similar symptoms, COVID-19 spreads more easily and causes more severe illness in some people compared to the seasonal flu. It also carries a higher risk of blood clots and long-term complications known as Long COVID.

Q: Do vaccines prevent me from getting COVID-19 completely?
A: No vaccine is 100% effective at preventing infection, especially as the virus evolves into new variants. However, vaccines are highly effective at preventing severe illness, hospitalization, and death, which is their primary goal.

Q: Do antibiotics treat COVID-19?
A: No, antibiotics only work against bacteria, not viruses. Taking antibiotics for a viral infection like COVID-19 will not help and can contribute to antibiotic resistance, though they may be prescribed if a secondary bacterial infection develops.

Q: How long am I contagious?
A: You are generally most contagious in the 2 days before symptoms start and for the first 5 days of illness. However, some people can remain contagious for 10 days or longer, particularly those with severe illness or weakened immune systems.

Q: What is Long COVID?
A: Long COVID refers to a wide range of new, returning, or ongoing health problems that people experience four or more weeks after being infected with the virus. These symptoms can affect many different organ systems and vary in intensity.