Cold, Flu or COVID-19 – How to Distinguish and Treat Respiratory Diseases

An increase in the morbidity rates for cold, flu and other respiratory infections is usually observed during autumn and winter. Some of these can be prevented by using vaccines. However, other infections require symptomatic treatment with medication. We talked to infectious diseases specialist, Professor Ligita Jančorienė from the Vilnius University Hospital Santaros Klinikos and the Faculty of Medicine at Vilnius University about all things relevant during the cold season – how to distinguish between respiratory diseases and how to know when antibiotics are actually needed or recommended.

What are the most common viral or bacterial respiratory diseases?

Respiratory tract infection is a rather broad term. Many viruses and some bacteria can cause respiratory infections. Among viral infections the best known is influenza, type A and type B. Such classification does not necessarily reflect the epidemiological patterns: an influenza A epidemic may develop first with subsequent growth in influenza B morbidity. Certain coronavirus strains have also been emerging and recognised worldwide; however, recently, the list of routine coronaviruses has been amended with the addition of SARS-CoV-2. The third common virus is respiratory syncytial virus (RSV), several different strains of which are known. The parainfluenza virus usually does not cause epidemics. Only isolated sporadic cases of parainfluenza have been reported; therefore, the parainfluenza morbidity pattern is characterised as endemic. Adenovirus respiratory infections are more commonly diagnosed in children. The respiratory symptoms of this infection are usually accompanied by conjunctivitis (an eye inflammation). Sometimes reoccurring adenovirus infections are reported manifesting as successive morbidity waves. Rhinovirus is a perennial virus that causes a runny nose. Less often reported viruses causing respiratory infections are metapneumovirus, bocavirus and some enteroviruses.

Pneumococcal pneumonia is the most common respiratory infection. Pneumococcus is most dangerous for small children – especially for those under the age of two. The risk of severe invasive pneumococcal infection is increases with age (from about 60 to 65 years of age). It is worth noting that according to the provisions of the National Vaccination Plan, free vaccination against pneumococcal infection is offered for those aged 75 or over. Legionellosis is another bacterial respiratory infection. The bacteria that cause it can be found in water supply systems, stagnant water, swimming pools, jacuzzies and so on. Other well-known bacterial respiratory infections are the mycoplasma infection and chlamydiosis.

Respiratory infections, especially those caused by viruses, are characterised by their seasonality. For instance, influenza or RSV infection in the northern hemisphere are more common in winter, and so in the southern hemisphere the winter season begins when it is summer in our region. Some viral respiratory infections can be also diagnosed during the warm season. There are also certain perennial infections caused by adenovirus or metapneumovirus, for example, that are not considered seasonal. The new coronavirus SARS-CoV-2 cannot be considered as seasonal as infections have been reported all year around.

Which infections – viral or bacterial – are more dangerous?

It is difficult to give a definitive answer. Each infection has its own character. The causative agent alone, does not predetermine the complexity of the disease (however, sometimes it is significant, as in the case of SARS-Co-V2, where at the beginning of the pandemic, before we had built up our immunity, we were “naked” in the face of this infection). Characteristics of the body getting viral or bacterial infections are of great importance. Influenza or pneumococcal infection may be fatal for the elderly or for people treated with immunosuppressants or those with many concomitant diseases. The general health condition of the individual is important.

Let’s talk about the symptoms: how can we distinguish a simple cold from flu or SARS-CoV-2?

The symptoms of upper respiratory infections can include a runny nose (rhinitis), inflammation of the ear (otitis), inflammation of the pharynx (pharyngitis), and sinusitis. The lower respiratory infections are usually characterised as bronchitis or pneumonia. Bronchitis is usually viral origin (especially in children), and pneumonia can be caused by viruses or bacteria. All of us probably remember very well the severe pneumonia cases caused by SARS-CoV-2 at the beginning of the pandemic. Such pneumonia can progress rapidly, resulting in respiratory failure or even death. Currently, after our exposure to the SARS-CoV-2 virus, our society has acquired partial herd immunity such that severe pneumonia cases have become less frequent and are usually diagnosed in elderly people with suppressed immune systems or the exacerbation of concomitant diseases.

The symptoms of a cold are characterised by a gradual onset, they are rather mild, not interfering with daily living and usually resolve spontaneously with time. Influenza develops rapidly and lasts longer than a cold, it interferes with daily living and can cause secondary complications, which are more severe than during the primary illness. Patients suffering from flu have to stay at home, in bed and visit their physician; hospitalisation is required in some cases, especially for the elderly. An influenza infection can often result in an inability to perform daily living activities or self-care, especially in elderly people, and there is also a risk of infection transfer to other people.

The pattern of the onset of symptoms (abrupt or gradual), as well as the incubation period (hours or days) and the time during which the patient is infectious should be considered during the diagnosis of infectious diseases. The usual symptoms are muscle ache, cough, fever, tiredness and diarrhoea. Changes in the sensations of taste and smell, as well as dyspnoea (difficulty with breathing), as well as other symptoms, like sneezing, a stuffy nose, sore throat and headache, are usually characteristic of a SARS-CoV-2 infection. Conversely, the influenza symptoms are very definite: a sudden onset of the condition, a brief incubation period with respiratory symptoms dominating and diarrhoea (more characteristic in children).

What treatment is prescribed in the case of respiratory infections? When are antibiotics necessary, and when can one recover without taking them?

First of all, it should be noted that antibiotics should only be prescribed by a treating physician after careful assessment of a patient’s condition. If the patient’s condition does not improve and the fever continues, with a productive cough, dyspnoea, and tightness of the chest develops, medical advice should be sought. In the case of severe forms, i. e. complicated flu (usually manifested by viral pneumonia), progression of the condition is very fast: Signs of respiratory failure or pneumonia become apparent on the second or third day. A patient’s condition worsening significantly is characteristic of viral pneumonia. If improvements in the condition alternate with it worsening, this is characteristic of bacterial complications. However, these can only be diagnosed by a physician on the basis of blood tests and some additional criteria.

When is the condition non-complicated, and when is it complicated? When symptoms are uncomplicated and similar to the flu (the term influenza-like illness is usually used to define it). If the patient is not elderly or an infant and has no risk factors, or concomitant diseases and does not take immunosuppressants, the uncomplicated influenza-like illness is treated using medication to control symptoms, fulfilling general requirements for infection control – personal protection measures, ventilation of the premisses, etc. However, if risk factors are identified, an antiviral treatment can be administered. Among all the viruses causing respiratory infections, the antiviral treatment is only available for influenza and SARS-CoV-2. In the case of influenza, antiviral medication available in Lithuania is prescribed both for children or adults and elderly people, as well as for pregnant women. For patients suffering from the COVID-19 infection, Nirmatrelvir/Ritonavir can be administered in an out-patient setting after the onset of symptoms, and if pneumonia and respiratory failure develops, another antiviral drug Remdesivir can be prescribed during in-hospital treatment. Nirmatrelvir/Ritonavir has been available in Lithuania since the spring of 2023. This treatment for the patient within the first five days after the onset of symptoms can be prescribed by a family doctor or a medical specialist providing consultations in a polyclinic or in-hospital emergency department. The treatment is prescribed for five days.

Specific treatment for other viral respiratory infections is not available. If a patient’s condition does not improve within 72 hours or even worsens, they should be referred to a physician or to an in-hospital admission department, where a decision regarding further treatment plans should be made. An influenza-like illness is characterised by a sudden onset, systemic symptoms – fever, weakness, headache, muscle aches with at least one respiratory symptom – a cough, sore throat, or dyspnoea. The above-mentioned symptoms are more pronounced in the case of severe acute respiratory disease, and then an in-hospital treatment is required. Flu infection can be suspected in all patients presenting with respiratory symptoms during the influenza season. If a patient's condition is not severe and there are no risk factors, antiviral drugs can be prescribed when signs of pneumonia develop (coughing up phlegm, chest discomfort and the disease has lasted for several days). Antibiotics are prescribed when examinations are carried out, and signs of secondary bacterial infection are reported. If there are risk factors, the patient should be brought to a physician or to an admission department. In the case of severe disease, when the condition is progressing, oxygen therapy is often required, and so, the patient should be hospitalised.

If symptoms characteristic of respiratory infections develop, usually the most relevant infections – SARS-CoV-2, flu (type A or B), or respiratory syncytial virus should be suspected. A physician will assess the patient’s complaints, condition and the risk of the condition progressing. Laboratory tests and radiological examinations should be carried out on the patient that presents in a moderate or progressing to severe condition. A very convenient scale to assess the heaviness of a patient’s condition has been used since the last pandemic – known as NEWS ( the National Early Warning Score). Patients vital parameters are assessed using this scale: breathing rate, oxygen saturation, systolic blood pressure, heart rate, consciousness and body temperature. After the assessment of these criteria, the final score is calculated. A final score higher than that indicates a high clinical risk of the disease, and the patient requires emergency care with the monitoring of vital functions. If the final score is lower, the patient can be discharged for further treatment and care in a home setting.

If there are no risk factors for severe disease, the symptoms are not severe, and the total NEWS score is less than 4, diagnostics are not usually required; it is sufficient to carry out rapid antigen test and the patient can be treated at home under the supervision of a family doctor. Currently the combined influenza and SARS-CoV-2 tests are available in the pharmacies and can be used for the primary diagnostics. If there are no risk factors, but the disease symptoms are severe, the first line treatment is antiviral drugs that can be prescribed by a family doctor for treatment as an out-patient. If, however, the patient has risk factors, the disease is not severe, antiviral drugs may also be helpful and a decision regarding the usefulness of additional tests – a general blood count, C - reactive protein and chest X-ray should be performed. The ultimate group of patients are those who have risk factors and severe disease. Such patients should be brought to the admissions department where a decision regarding patient's hospitalisation should be made. Nevertheless, if there are no indications for when the antibacterial treatment, or treatment with antiviral drugs should be initiated. Usually, the patient is hospitalised in the case of diagnosed respiratory failure, severe dehydration, disorders of the central nervous system, acute renal failure and blood pressure changes or flare-ups of underlying chronic disease and other severe health disorders.

When should the rapid antigen test be used?

The rapid antigen tests are the most informative at the onset of the infection when the virus concentration has reached its highest levels. The test can be done on the second or third day of symptoms at the latest. For instance, the SARS-CoV-2 test is most effective on the second day (evidence has shown). The test itself has been refined during the last pandemic period, is very reliable and widely used both in an out-patient and in-hospital setting. As a result, a molecular test is not always necessary to confirm a diagnosis, as the rapid antigen test is sufficient. The combined rapid antigen tests can be used to diagnose SARS-CoV-2, RSV, and influenza A and B.

Let's talk about vaccines: when are they useful, and when should we refrain from vaccination?

We have flu vaccines that contain 3 or 4 components (currently there are 4-component vaccines). Flu vaccines are updated annually. The World Health Organisation has established the Flu Monitoring Network. Changes in the influenza virus have been monitored for more than 100 years. Data are collected and possible flu virus strains that will circulate during the next flu season are predicted by applying a mathematical prediction model. Despite the technologies used for the production of flu vaccines for the northern hemisphere (there are 5-6 main producers), the antigenic content is the same. Each year, at the end of February or the beginning of March, the PSO announces the information about the recommended content of the vaccines. The vaccines are produced according to these recommendations. It is recommended that we get vaccinated before the flu season starts, usually before the middle of September. An annual vaccination with the updated flu vaccine is recommended, as the vaccine is continuously updated according to the virus strains most expected to circulate during the coming season.

Actually, vaccination is recommended for all groups of people without exception. For the people in the following groups, the cost of vaccination is reimbursed by the Government. The PSO recommends flue vaccination for pregnant women (during any trimester of pregnancy), for children from 6 months to 5 years, to people above 65 years, and those suffering from chronic diseases. Healthcare professionals are also considered as a high-risk group. Vaccinations are available to anyone who does not want to spend time absent from work or suffer from illness because of a flu infection.

Currently, the same recommendations are applicable for vaccination against SARS-CoV-2. The new XBB vaccine is available for every citizen of Lithuania. If anyone has not had a confirmed SARS-CoV-2 infection during 2023, the immunity against this infection will not have been boosted, therefore vaccination with the XBB vaccine is recommended. It protects against the Omicron XBB strain and its sub-variants. However, if someone had recently been confirmed with an SAES-CoV-2 infection, it is most likely, that they were exposed to Omicron strain, which was used for vaccine production. In this case, vaccination is not necessary, the immunity has already boosted. It is difficult to make a prognosis, however, it is possible that the SARS-CoV-2 virus vaccine will become a routine vaccine, similar to the currently available flu vaccines.