K224 / K225 / 2027

Lesson 2 of 5 / Infectious diseases in humans

Influenza and pneumococcal disease

Can similar symptoms have different pathogens?

I can identify the causes and typical signs or symptoms of influenza and pneumococcal disease.

  • I can state causes, signs and symptoms of influenza and pneumococcal disease.Syllabus

    Syllabus K224 / K225, Topic 7(c). State causes, signs and symptoms of influenza and pneumococcal disease.

About 5 min

Make a guess. You are not marked.

Two classmates both have a fever and a cough. Must they have the same disease?

  1. Different pathogens can cause the same symptoms.
  2. The same symptoms mean the same pathogen.
  3. They must if they fell ill on the same day.
Show the answer

Different pathogens can cause the same symptoms.

Influenza is caused by a virus and pneumococcal disease by a bacterium, yet both can cause fever and cough.

The key idea

Influenza is caused by influenza viruses; pneumococcal disease is caused by pneumococcus bacteria. Their symptoms can overlap.

Can the same symptom have different causes?
Respiratory tract highlighted
Cause
Influenza virus
Typical features
Cough, fever/chills, aches, fatigue

Purple symbols: viral cause. Green symbols: bacterial cause. Positions indicate possible affected regions, not a diagnostic scan. Cough and fever overlap and cannot establish the cause by themselves.

Explanation

Influenza (flu) is an infectious disease of the airways caused by influenza viruses. Common symptoms are cough, sore throat, fever, headache, aching muscles and tiredness. Symptoms often start suddenly, but not everyone has all of them.

Pneumococcal disease is caused by the bacterium Streptococcus pneumoniae, also called pneumococcus. It can cause pneumonia (an infection of the lungs), ear infections and meningitis. The symptoms depend on where the infection is.

Pneumococcal pneumonia can cause fever, cough, chest pain and fast or difficult breathing. Other bacteria and viruses can also cause pneumonia.

A symptom is something the person feels, such as a headache. A sign is something others can see or measure, such as a high temperature. Different diseases share many signs and symptoms, so a list of symptoms cannot tell you which pathogen is the cause.

Step by step
  1. 1

    Name the specific disease

    Distinguish influenza, pneumococcal disease and the broader term pneumonia.

  2. 2

    Name its pathogen type

    Influenza is viral; pneumococcal disease is bacterial.

  3. 3

    Describe without diagnosing

    Give relevant typical signs or symptoms, while recognising their overlap.

Worked example

A shared cough and fever

Two fictional cases both include cough and fever. Does this prove that both have influenza?

One way to explain it

No. These features can occur in influenza and in other infections, including pneumococcal pneumonia. They do not establish which pathogen is present.

Why this answer works
  • A shared effect does not establish a shared cause.
  • Use the named bacterial and viral examples.
  • Avoid a diagnosis unsupported by the evidence.

Watch out for this

A student says: "Pneumonia always means infection by pneumococcus." What is wrong with this?

Show the answer

Pneumococcus can cause pneumonia, but other bacteria and viruses can also cause it. Pneumococcal disease also includes infections at other sites.

Check your understanding

Which comparison is correct?

  1. Influenza is viral; pneumococcal disease is bacterial; symptoms may overlap.
  2. Both are caused by viruses, because both give a fever and a cough at the start.
  3. Every lung infection is caused by pneumococcus.
Show the answer

Influenza is viral; pneumococcal disease is bacterial; symptoms may overlap.

Distinguish the causes even when both illnesses include cough and fever.

Quick recall

Card 1 of 3. Answer in your head, then check.

Can similar symptoms have different pathogens?

You can return to this lesson any time.