Lesson 3 of 6 / Infectious diseases
Influenza and pneumococcal disease
Can similar symptoms have different pathogens?
In this lesson: Identify the causes and typical signs or symptoms of influenza and pneumococcal disease.
About 5 min
The key ideaInfluenza is caused by influenza viruses; pneumococcal disease is caused by pneumococcus bacteria. Their symptoms can overlap.
- Cause
- Influenza virus
- Typical features
- Cough, fever/chills, aches, fatigue
Influenza is viral. Not every case has every listed symptom or a fever.
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 is a respiratory infectious disease caused by influenza viruses. Typical symptoms include cough, sore throat, fever or chills, headache, muscle aches and tiredness. Symptoms often begin suddenly, but not every affected person has every symptom or a fever.
Pneumococcal disease is caused by the bacterium Streptococcus pneumoniae, also called pneumococcus. It can cause different infections, including pneumonia, middle-ear infection and meningitis. The signs and symptoms depend on the site of infection.
For pneumococcal pneumonia, features can include fever or chills, cough, chest pain and rapid or difficult breathing. Pneumonia is an infection of the lungs that can have several causes; not all pneumonia is pneumococcal.
A symptom is experienced by the person, such as a headache. A sign is an observable or measurable change, such as a measured high temperature. Because signs and symptoms overlap between diseases, a short list cannot reliably identify the pathogen. Examination questions should provide the relevant cause or evidence when asking for a specific mechanism.
Step by step
- 1
Name the specific disease
Distinguish influenza, pneumococcal disease and the broader term pneumonia.
- 2
Name its pathogen type
Influenza is viral; pneumococcal disease is bacterial.
- 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.
Is this true? "Pneumonia always means infection by pneumococcus."
Pneumococcus can cause pneumonia, but other bacteria and viruses can also cause it. Pneumococcal disease also includes infections at other sites.