Medical

Seasonal influenza causes sudden fever, dry cough, headache, muscle-joint pain, sore throat and runny nose.

The pathogen

Influenza Kills 646,000-700,000 People Worldwide Each Year

H1N1

There are 4 types of seasonal influenza viruses, types A, B, C and D. Influenza A and B viruses circulate and cause seasonal epidemics of disease.

Influenza A viruses are further classified into subtypes according to the combinations of the hemagglutinin (HA) and the neuraminidase (NA), the proteins on the surface of the virus. Currently circulating in humans are subtype A(H1N1) and A(H3N2) influenza viruses. The A(H1N1) is also written as A(H1N1)pdm09 as it caused the pandemic in 2009 and subsequently replaced the seasonal influenza A(H1N1) virus which had circulated prior to 2009.

Only influenza type A viruses are known to have caused pandemics.

Influenza B viruses are not classified into subtypes, but can be broken down into lineages. Currently circulating influenza type B viruses belong to either B/Yamagata or B/Victoria lineage.

Influenza C virus is detected less frequently and usually causes mild infections, thus does not present public health importance.

Influenza D viruses primarily affect cattle and are not known to infect or cause illness in people.

COVID-19 is caused by infection with a new coronavirus (called SARS-CoV-2)

Signs and symptoms

Seasonal influenza is characterized by a sudden onset of fever, cough (usually dry), headache, muscle and joint pain, severe malaise (feeling unwell), sore throat and a runny nose. The cough can be severe and can last 2 or more weeks. Most people recover from fever and other symptoms within a week without requiring medical attention. But influenza can cause severe illness or death especially in people at high risk (see below).

Illnesses range from mild to severe and even death. Hospitalization and death occur mainly among high risk groups. Worldwide, these annual epidemics are estimated to result in about 3 to 5 million cases of severe illness, and about 290 000 to 650 000 respiratory deaths.

The effects of seasonal influenza epidemics in developing countries are not fully known, but research estimates that 99% of deaths in children under 5 years of age with influenza related lower respiratory tract infections are found in developing countries.

Signs and symptoms of COVID-19 may include change in or loss of taste or smell.Typically, a person develops symptoms 5 days after being infected, but symptoms can appear as early as 2 days after infection or as late as 14 days after infection, and the time range can vary.

Epidemiology

All age groups can be affected but there are groups that are more at risk than others.

People at greater risk of severe disease or complications when infected are: pregnant women, children under 59 months, the elderly, individuals with chronic medical conditions (such as chronic cardiac, pulmonary, renal, metabolic, neurodevelopmental, liver or hematologic diseases) and individuals with immunosuppressive conditions (such as HIV/AIDS, receiving chemotherapy or steroids, or malignancy).

Health care workers are at high risk acquiring influenza virus infection due to increased exposure to the patients and risk further spread particularly to vulnerable individuals.
In terms of transmission, seasonal influenza spreads easily, with rapid transmission in crowded areas including schools and nursing homes. When an infected person coughs or sneezes, droplets containing viruses (infectious droplets) are dispersed into the air and can spread up to one meter, and infect persons in close proximity who breathe these droplets in. The virus can also be spread by hands contaminated with influenza viruses. To prevent transmission, people should cover their mouth and nose with a tissue when coughing, and wash their hands regularly.

In temperate climates, seasonal epidemics occur mainly during winter, while in tropical regions, influenza may occur throughout the year, causing outbreaks more irregularly.

The time from infection to illness, known as the incubation period, is about 2 days, but ranges from one to four days.

Diagnosis

The majority of cases of human influenza are clinically diagnosed. However, during periods of low influenza activity and outside of epidemics situations, the infection of other respiratory viruses e.g. rhinovirus, respiratory syncytial virus, parainfluenza and adenovirus can also present as Influenza-like Illness (ILI) which makes the clinical differentiation of influenza from other pathogens difficult.

Rapid influenza diagnostic tests (RIDTs) are used in clinical settings, but they have lower sensitivity compared to RT-PCR methods and their reliability depends largely on the conditions under which they are used.

When Flu Spreads

People with flu can spread it to others up to about 6 feet away. Most experts think that flu viruses spread mainly by droplets made when people with flu cough, sneeze or talk. These droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs. Less often, a person might get flu by touching a surface or object that has flu virus on it and then touching their own mouth, nose, or possibly their eyes.

Both COVID-19 and flu can spread from person-to-person, between people who are in close contact with one another (within about 6 feet).COVID-19 is more contagious among certain populations and age groups than flu.

People with flu are most contagious in the first three to four days after their illness begins. Most healthy adults may be able to infect others beginning 1 day before symptoms develop and up to 5 to 7 days after becoming sick. Children and some people with weakened immune systems may pass the virus for longer than 7 days.

If someone is asymptomatic or their symptoms go away, it’s possible to remain contagious for at least 10 days after testing positive for COVID-19

Symptoms can begin about 2 days (but can range from 1 to 4 days) after the virus enters the body. [ Centers for Disease Control and Prevention, National Center for Immunization and Respiratory Diseases (NCIRD)]

Both COVID-19 and flu can result in complications, including:

Pneumonia
Respiratory failure
Acute respiratory distress syndrome (i.e. fluid in lungs)
Sepsis
Cardiac injury (e.g. heart attacks and stroke)
Multiple-organ failure (respiratory failure, kidney failure, shock)
Worsening of chronic medical conditions (involving the lungs, heart, nervous system or diabetes)
Inflammation of the heart, brain or muscle tissues

Secondary bacterial infections (i.e. infections that occur in people who have already been infected with flu or COVID-19)

Additional complications associated with COVID-19 can include:

Blood clots in the veins and arteries of the lungs, heart, legs or brain Multisystem Inflammatory Syndrome in Children (MIS-C)


Source:

  1. WHO
  2. American College of Chest Physicians
  3. American College of Emergency Physicians
  4. American Society of Hematology
  5. American Thoracic Society
  6. Biomedical Advanced Research and Development Authority
  7. Centers for Disease Control and Prevention
  8. Food and Drug Administration
  9. Infectious Diseases Society of America
  10. National Institutes of Health
  11. Pediatric Infectious Diseases Society
  12. Society of Critical Care Medicine
  13. Society of Infectious Diseases Pharmacists.

 

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