Differential diagnosis: cold, flu or COVID-19?

As the days become shorter and the temperature falls, the frequency of seasonal viral infections — such as cold and influenza (flu) — increases. Cold and flu share some symptoms and, if managed effectively, are often self-limiting and resolve within a couple of weeks in people without pre-existing conditions. However, some of their symptoms are similar to those seen in COVID-19 infections, which will present a challenge for healthcare professionals.

This winter, an increasing number of patients will likely present in pharmacy and primary care with symptoms of a viral infection, and be justifiably concerned about what the next steps — with regard to managing their symptoms — should be. Therefore, it is necessary that pharmacists and pharmacy teams can recognise, reassure and refer patients appropriately.

This article provides an overview of the main differences between the symptoms for cold, flu and COVID-19, to better equip pharmacy teams to use their professional judgement when it comes to advising patients on treatment and/or referral. For a visual summary of the main differences between the symptoms of colds, flu and COVID-19, download this printable resource.

COVID-19

Symptoms

The novel coronavirus SARS-CoV-2, commonly referred to as COVID-19, typically causes mild upper respiratory infections
^[1]
.

The main symptoms include:

• A high temperature — the skin feels hot to touch on the chest or back;
• A new, continuous cough — coughing a lot for more than one hour, or three or more coughing episodes in 24 hours (if a patient usually has a cough, it may be worse than usual);
• A loss or change in sense of smell or taste^[2]
  .

Most people with coronavirus will have at least one of these symptoms, with the severity ranging from mild to severe^[2]
.

Gathering information and providing advice

When speaking with a patient who has any one of these symptoms, either during a remote consultation or face-to-face, there is a need to find out more information and provide appropriate advice — for example, by asking:

• Can you describe your symptoms?

Most common presentations of COVID-19 include a dry cough (although sputum production is not uncommon), fever (up to 50% of patients do not have a fever at presentation), or a loss or change to sense of smell or taste^[2],[3]
.

• Have you experienced a loss or change in your sense of smell or taste?

Although this symptom can occur in cold and flu (e.g. as a result of congestion, which is present in around 5% of COVID cases), a change in smell or taste is a common symptom of COVID-19. If this is the case, the patient should be advised to obtain a test and self-isolate, along with their household and support bubble^[2],[3],[4]
.

• How suddenly did your symptoms begin?

The incubation period for COVID-19 is up to 14 days and symptoms range from mild to severe^[5]
. Cold symptoms appear gradually, while flu symptoms come on very quickly^[6],[7]
.

• Have you been in contact with anyone who has either tested positive for, or has clinically suspected, COVID-19?
• Is anyone in your immediate family, or those you live with, unwell, or has anyone tested positive for COVID-19 or had symptoms of COVID-19 in the last 14 days?

If the patient has been in contact with a person with suspected COVID-19 or who has tested positive, pharmacists and pharmacy teams should advise them to self-isolate at home for 14 days from the date of their last contact with that person, even if they are not displaying symptoms^[4]
. As the incubation period for COVID-19 is up to 14 days, it is very important that the patient follows this even if they feel well^[5],[4]
. Patients should be advised that their household does not need to self-isolate with them if they do not have symptoms of COVID-19, but they should take extra care to follow the guidance on social distancing, handwashing and respiratory hygiene^[4]
.

However, if the patient develops symptoms while self-isolating, they should stay at home for at least ten days from when their symptoms started and arrange to have a test via the government website^[4],[8]
.

Advise patients that tests can be carried out within the first five days of symptom onset. On days one to four, patients can get tested at a site or at home; however, on day five, patients will need to go to a test site^[8]
.

If the patient does not develop symptoms of COVID-19, they should not arrange to undergo testing^[4]
.

• Are you waiting for a COVID-19 test or the results?

If patients are awaiting their result, then there is a chance they could have contracted COVID-19. They should be advised to self-isolate until they receive their results or for at least 10 days from the onset of symptoms (as above). If the patient is presenting after day five of the onset of their symptoms, they should be advised it is too late to obtain a test and that they should self-isolate, along with their household and support bubble^[9]
.

Applying clinical and professional judgement

Considering the answers to these questions and the symptom comparison Table, pharmacists and their teams should use their professional judgement to determine whether the patient’s symptoms are indicative of COVID-19^{[2],[6],[7],[10],[11]}
. If the patient has presented directly to the pharmacy and COVID-19 infection is suspected, pharmacists and pharmacy teams should follow the NHS standard operating procedure^[12],[13]
.

If the symptoms are not indicative of COVID-19, cold and flu summaries, and useful resources from The Pharmaceutical Journal
, can be used to aid differential diagnosis.

Table. Comparison of COVID-19, flu and cold symptoms

Colds

Symptoms

A cold is caused by a mild viral infection of the nose, throat, sinuses and upper airways^[6]
.

Children aged under six years are at greatest risk of colds, but healthy adults can also expect to have two or three colds annually^[14]
.

Symptoms usually appear gradually and include:

• A sore throat;
• A blocked or runny nose;
• Sneezing;
• A cough;
• A raised temperature^[6],[14]
  .

Generally, patients may feel unwell but are able to continue daily activities as normal.

More severe symptoms, including headache and aching muscles, can also occur, although these are generally associated more with flu. Symptoms usually resolve within one to two weeks^[6],[14]
.

Gathering information and providing advice

When speaking with a patient who has any of these symptoms, either during a remote consultation or face-to-face, there is a need to find out more information and provide appropriate advice — for example, by asking:

• How suddenly did the symptoms begin?
• Are you able to smell and taste as normal?
• What management strategies (if any) have you tried so far? Did any help?

Considering the answers to these questions and the symptom comparison Table, pharmacists and their teams should use their professional judgement to determine if symptomatic relief and self-care measures are enough, or if there are red flags that prompt the need to refer.

Reassure the patient that the symptoms they are experiencing are likely to be a cold, therefore they do not need to self-isolate or obtain a COVID-19 test.

Following the ‘Cold and flu consultation pathway for community pharmacy’, patients should also be advised on appropriate infection control and self-care measures and the antimicrobial stewardship message that viral infections are not treated with antibiotics, alongside a discussion on the suitability of pharmacological options that may help relieve their symptoms.

Influenza

Symptoms

Flu symptoms typically come on very quickly (within a few hours) and tend to be more widespread than those seen in a cold. These may include:

• A sudden fever – a temperature of 38C or above;
• An aching body;
• Feeling tired or exhausted;
• A dry cough;
• A sore throat;
• A headache;
• Difficulty sleeping;
• Loss of appetite;
• Diarrhoea or stomach pain;
• Feeling sick and being sick^[7]
  .

The symptoms are similar for children, but they can also experience pain in their ear and appear less active. Patients with flu will likely describe feeling exhausted and too unwell to carry on daily activities as normal^[7]
.

Gathering information and providing advice

When speaking with a patient who has any of these symptoms, either during a remote consultation or face-to-face, there is a need to find out more information and provide appropriate advice — for example, by asking:

• Have you recently been in contact with people with flu?
• Have you been vaccinated against the flu?
• How suddenly did your symptoms begin?
• Are you able to smell and taste as normal?
• What management strategies (if any) have you tried so far? Did any help?

Considering the answers to these questions and the symptom comparison Table, pharmacists and pharmacy teams should use their professional judgement to determine if symptomatic relief and self-care measures are enough, or if there are red flags that prompt the need to refer. As flu is very infectious and easily spread to other people, especially within the first five days of infection, patients should be advised on infection control and self-care measures as outlined in the ‘Cold and flu consultation pathway for community pharmacy’.

Reassure the patient that the symptoms they are experiencing are likely to be related to influenza, therefore they do not need to obtain a COVID-19 test. Explain that, as a viral infection, flu is not to be treated with antibiotics; however, a discussion on the suitability of pharmacological options that may help relieve their symptoms would be warranted.

As a preventative measure, pharmacists and pharmacy teams should also recommend that the patient receives the flu vaccine before the start of next year’s flu season — explaining that contracting it this year does not confer immunity next year.

Best practice

Owing to the potential for symptoms of colds and flu to be confused with COVID-19, it is more important than ever that pharmacists and pharmacy teams feel confident advising patients on the management of their respiratory conditions. As the potential strain on the NHS this winter could be severe, it is important to understand when it is and is not appropriate to refer a patient.

This article and the useful resources below aim to support best practice in this area, particularly for cold and flu consultations.