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VERIFIED CONTENTAuthor: Katarzyna Wieczorek-SzukaƂa, MD, PhD, medical biotechnologist, Medical University of Lodz

In the era of a pandemic, most of us wonder if it is possible to distinguish the symptoms of a common cold or an allergic reaction from infection with the SARS-CoV-2 virus. Many common infections show little specific symptoms that are similar to those seen in most COVID-19 cases. What should you first pay attention to? Which diseases can be confusingly similar to COVID-19?

Characteristic symptoms of COVID

The symptoms of COVID-19 largely depend on the genetic variant of the virus that is causing the infection. Last season, the Alpha and Beta strains dominated, and the developing infection had in most cases common symptoms, such as:

  • headaches and muscle aches,
  • chronic fatigue and weakness,
  • high fever,
  • dry cough,
  • loss of smell and taste.

It is the latter ailments related to the temporary lack of any taste and smell (despite the lack of a runny nose) that were one of the most characteristic symptoms of SARS-CoV-2 infection. In more severe cases of complications, especially in the elderly or with comorbidities, the following was observed:

  • severe pneumonia,
  • severe breathlessness,
  • loss of consciousness,
  • fainting,
  • severe neurological damage.

As the pathogen stays in the environment, its genetic sequence changes, new mutations and genetic variants of the virus arise. Since 2022, the delta variant has become the predominant mutation, which also causes slightly different symptoms than its previous versions. Taste and smell disorders are now very rare, but the first symptoms of a developing infection are:

  • severe headache,
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  • sore throat,
  • nausea or vomiting,
  • lack of appetite,
  • hearing impairment.

5 diseases that can be confused with COVID-19

1. Angina

Angina is an acute inflammation of the pharyngeal mucosa and tonsils. This infection can be viral or bacterial in origin. The overwhelming majority of cases of angina are caused by such groups of viruses as: rhinoviruses, adenoviruses andcoronaviruses (from which SARS-CoV-2 is also derived). Angina is also caused by streptococcal bacteria from the group Streptococcus pyogenes. Most often, children and adolescents up to the age of 15 suffer from angina, especially in the autumn and winter period.

The viral and bacterial variants of angina may differ in the intensity and speed of the symptoms. Viral angina is characterized by its gradual, slow intensification, while bacterial infection has a faster and more rapid course.

The common symptoms of both variants, which may be especially confused with infection with the Delta SARS-CoV-2 variant, include:

  • general feeling of weakness and "broken",
  • severe pain and swelling in the throat,
  • cough,
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  • fever,
  • muscle aches,
  • diarrhea and nausea.

When diagnosed by a specialist, streptococcal angina is easier to distinguish from COVID-19 than the viral variant. Its symptoms are usually more strongly associated with acute pain, hyperemia and reddening of the throat as well as the appearance of white and yellow patches on the tonsil mucosa.

Often in the course of streptococcal angina, purulent discharge from the paranasal sinuses and on the walls of the pharynx appears, and the cervical lymph nodes are significantly enlarged.

Angina is a highly contagious disease. The infection usually occurs through droplets or through direct contact with secretions from the patient's throat or nose.

2. Flu

Flu is very often confused with a cold due to some of the similar symptoms. However, it must not be underestimated, because it is a much more serious infection, and complications from the flu can even lead to damage to the heart muscle or meningitis.

Flu is caused by three types of flu virus belonging to the orthomyxovirus family: A, B and C.

Type A and B viruses cause serious illnesses that in the past have even reached epidemic proportions (e.g. the Spanish epidemic during World War II, Asian and Hong Kong flu pandemics in the 1950s, and the 2009 Mexican flu pandemic year). Variant C of the virus causes illnesses of a milder course.

The most common clinical symptoms of developing flu are:

  • sudden onset of high fever,
  • chills,
  • muscle and joint pain,
  • fatigue and weakness,
  • dry cough.

As you can see, these symptoms are confusingly similar to the SARS-CoV-2 virus infection, especially since the current Delta variant usually does not cause loss of smell and taste disturbances, which inmade it possible to distinguish these two infections to some extent.

Even mild flu is often associated with bacterial complications causing pneumonia. This condition can have the same symptoms as complications accompanying COVID-19:

  • feeling short of breath,
  • chest tightness,
  • feeling of hypoxia,
  • dizziness and fainting.

The only potential difference between the flu and COVID-19 may be the incubation time - the time it takes from the virus enters the body until the first symptoms of the disease appear. In the case of the flu, this time is usually short, about 2 to 3 days, while the development of COVID-19 symptoms usually takes longer - about 5 to 7 days. However, this is not a characteristic feature as it largely depends on the patient's individual immunity.

3. Cold

The common cold is the most common infectious disease in humans. Colds can be caused by over 200 different types of viruses.

The most common infection is rhinoviruses, but also coronaviruses, adenoviruses, enteroviruses or RSV virus, and in some cases also several different viruses acting simultaneously. These pathogens are most often transmitted by airborne or droplet contact after contact with the secretions of an infected person.

The increase in the incidence is recorded - similar to COVID-19 - in the fall and winter season - when most of us spend more time in closed, dry rooms. Most likely, the low air humidity allows for greater dispersion of virus particles and thus more efficient infection.

Symptoms of a classic cold - unlike the flu - usually develop gradually, within 2 to 4 days of infection, and usually disappear spontaneously after about a week. Very rarely, in adults with colds, a sudden increase in body temperature is observed, and the main symptoms are:

  • Qatar,
  • cough,
  • sore throat,
  • loss of appetite.

During this type of infection, muscle and joint pain, as well as chronic fatigue and weakness of the body, so characteristic of flu or COVID-19, are unlikely to occur. The common cold is usually less severe than the flu, but the indeterminate symptoms are practically impossible to distinguish from the mild course of SARS-CoV-2 infection.

Therefore, in case of doubt - especially in the period of winter immunity drops - it is always best to perform a diagnostic test that will clearly identify the source of infection.

4. Food poisoning

WIf you eat stale or raw food, you may experience acute gastrointestinal complaints, also known as food poisoning. The number of food poisonings increases especially in summer, when the increase in temperature also creates better conditions for the growth of bacteria.

The most common causes of stomach ailments are bacteria of the genus Campylobacter, Escherichia coli, Salmonella, Shigella, and Clostridium. The toxins released by them trigger a strong immune system response, causing:

  • stomach aches and nausea,
  • vomiting,
  • diarrhea.

With more severe poisoning, you may also experience severe fever and chills, muscle pain and general weakness.

It turns out that many patients with mild COVID-19 show very similar symptoms. The results of the research indicate that in the case of the Delta variant, in over 50% of patients, gastrointestinal complaints constitute a set of initial symptoms of coronavirus infection.

It takes about 2 days for nausea, vomiting or diarrhea to subside, but fever, weakness or shortness of breath appear - that is, more typical symptoms associated with the flu or a cold.

The feature that can distinguish typical food poisoning from infection with SARS-CoV-2 virus is its shorter and less complicated course.

If gastrointestinal complaints appear several to several hours after eating a potentially stale product (most often milk, eggs, raw meat) and disappear after about 2-3 days - most likely we are dealing with ordinary "indigestion" caused by bacterial toxins in food.

However, if the patient's well-being worsens, further diagnostics will be necessary, e.g. for the presence of botulinum toxins, but also for COVID-19.

5. Allergies

An allergy is nothing more than the hypersensitivity of the immune system to foreign substances called allergens, such as pollen, mites, animal proteins or chemicals. An over-stimulated immune system produces dozens of antibodies, cells and substances (e.g. histamine) that cause inflammation and numerous clinical symptoms.

One of the most common types of allergies is the so-called allergic rhinitis, also known as hay fever, which also manifests itself in:

  • watery and itchy eyes,
  • watery nasal discharge,
  • itchy nose and throat,
  • fits of sneezing.

Symptoms most often occur in the spring and summer seasons, when the concentration of pollen in the air reaches its maximum. However, in people who are allergic to othersallergens present in our homes, such as mold spores, animal hair or dust, ailments can persist even throughout the year. An additional symptom, common in allergy sufferers, may also be attacks of dry cough and shortness of breath that increases after contact with the allergen.

The above-mentioned symptoms may become more annoying when a new factor appears at home - an allergen - with which the patient's body has not been in contact so far - e.g. a new animal, foods such as seafood or nuts, and even quilts or mattresses .

Distinguishing the above symptoms from the mild course of COVID-19 infection can be extremely difficult in practice, especially if a person has been suffering from an allergy for many years. It is worth noting, however, that in allergic reactions there is rather no loss of taste or smell, as is the case with coronavirus infection (mainly types Alpha and Beta). There is also no fever and typical for COVID-19 muscle pain, as well as chronic fatigue and weakness.

If in doubt whether the escalating allergy-like symptoms may be caused by SARS-CoV-2 infection, the best solution is to perform a molecular test immediately. Thanks to this, it will be possible to take appropriate measures as soon as possible to prevent the infection of other people, and also shorten or alleviate the course of the disease.

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