Overview

Viral and bacterial infections and diseases have caused a massive effect on our lives, ranging from mild flu to more severe illnesses that can even result in death.¹ In this article, we will discuss influenza and pneumonia and how they differ.

So, what is influenza? It is usually referred to as the flu and causes mild to severe illnesses.² It is an acute respiratory infection and affects us worldwide.³ There are different types and pandemics related to influenza that we will further discuss in the sections below.

The next part of this article is about pneumonia. To put it short, it is an inflammation of the lungs due to infection.⁴ As with influenza, pneumonia can be either mild or severe, with some individuals being more susceptible than others (such as the elderly and children).⁴ Further information about pneumonia will be discussed in this article as well.

Influenza

Overview and Origin

Influenza, or the flu, is a respiratory infection that has caused multiple pandemics in the past – the first one was known as the Spanish flu in 1918 and was caused by influenza A(H1N1) virus.⁵ Other forms of influenza include A(H2N2) virus (Asian flu, 1957), A(H3N2) virus (Hong Kong flu, 1968), and A(H1N1)pdm09 virus (swine flu, 2009).⁵ At the present date, A(H1N1)pdm09 and A(H3N2) viruses along with influenza B virus (Yamagata and Victorian lineages) cause seasonal flu, but the A(H1N1) and A(H2N2) viruses no longer appear.⁵ 

The influenza virus is a negative-strand RNA virus and has 4 distinct types: influenza A, B, C and D:

• Influenza A: infects different species like humans, swine, horses, and birds. It is more capable of mutations and antigenic variation than the other types making it the major cause of pandemics. It is the most virulent and can cause death^3,6
• Influenza B: causes seasonal flu epidemic in humans⁶
• Influenza C: does not cause an epidemic and only causes mild symptoms⁶
• Influenza D: infects sheep, swine, and cattle. It is not seen to cause disease in humans⁶

Symptoms, complications and risk factors

There are multiple symptoms associated with influenza and they include:^2,7

• Fever/chills
• Dry cough
• Sore throat
• Runny nose
• Muscle and body aches
• Headache
• Sleep difficulties
• Diarrhoea (more common in children)
• Fatigue

Influenza usually causes uncomplicated infections that persist for 2-8 days.³ However, a set of patients, mostly children, elderly and people with pre-existing illnesses (e.g. kidney and liver disease, asthma, sickle cell anaemia) may experience complications due to viral or secondary bacterial pneumonia with respiratory/multiorgan failure.³ Some of the other complications are listed in Table 1.³

Table 1. Complications of influenza

Diagnosis and treatment

It is hard to distinguish flu from other viral or bacterial infections in the lungs using symptoms alone.² Hence more diagnostic tests are required, such as ‘rapid influenza diagnostic tests’ (RIDTs). RIDTs operate by testing for the viral antigens that cause an immune response.⁸ However, RIDTs are not as accurate as other tests e.g. ‘rapid molecular assays’. Rapid molecular assays are used to detect the genetic material of the influenza virus.⁸

Once faced with influenza, there are a few things that can be done to treat it:^2,7

• Plenty of rest
• Taking pain killers
• Staying hydrated
• Antiviral drugs

Prevention

There are a few steps that can be taken to prevent the spread of infection with influenza:^2,7

• Wash hands regularly
• Avoid contact with sick individuals
• Taking flu vaccines
• Covering coughs/sneezes
• Bin tissues as soon as they are used

Pneumonia

Overview and Origin

Pneumonia is a big health concern that is linked to short and long-term mortality.⁹ It is the leading cause of death among all ages worldwide in the infectious disease department.⁹ In severe pneumonia cases, patients that survive have significant changes such as alteration of the lung function, reduced mental and cognitive functions, fatigue and even reduced motor function.⁹

Generally, pneumonia is linked to infection, however pathologically speaking it is any inflammatory process that involves the alveolar spaces.¹⁰ There are different types of pneumonia:⁹ 

CAP (Community-acquired pneumonia)

There are multiple risk factors for CAP such as age and gender, and medical conditions like autoimmune and heart diseases, which affect the identification of CAP.¹¹

HAP (Hospital-acquired pneumonia) 

This is a common infection in hospitals and is considered the second most common nosocomial infection which causes inflammation in the parenchyma. It is commonly encountered in patients who have been in the intensive care unit (ICU) for at least 48 hours.¹¹

VAP (Ventilator-associated pneumonia)

This is considered one of the deadliest nosocomial infections. VAP develops within 48-72 hours after the placement of artificial airways for mechanical ventilation in the patient.¹¹ 

There are different causative agents for pneumonia; for example, Streptococcus pneumoniae, Staphylococcus aureus, Pseudomonas aeruginosa and, Klebsiella pneumoniae (which can also be a causative agent for HAP).¹¹ 

In cases of VAP, the intubation can become a breeding ground for bacteria and thus lead to pneumonia.¹¹ Pseudomonas aeruginosa, Klebsiella pneumoniae, Acinetobacter baumannii and, Staphylococcus aureus (including MRSA) are some of the causing agents for VAP.¹¹ Pneumonia can also develop due to a viral infection rather than a bacterial origin, like influenza.¹²

Symptoms and complications

When pneumonia occurs, there are several symptoms associated with it including:¹²

• Fever
• Cough with yellow, greenish or even bloody mucus
• Shortness of breath
• Chills and sweating
• Shallow breathing
• Sharp/stabbing chest pain that worsens upon deep breathing or coughing
• Loss of appetite
• Nausea/vomiting
• Confusion (mostly in the elderly)

In addition, some complications can arise in patients with pneumonia such as:¹³

• Sepsis
• Acute respiratory distress
• Heart failure
• Arrhythmias
• Encephalitis
• Pulmonary abscess
• Endocarditis
• Cholestatic jaundice
• Pericarditis
• Myocarditis

Diagnosis and treatment

To diagnose pneumonia, the symptoms and patient history are taken along with a physical examination.¹¹

It is important to have the proper diagnosis as other conditions may mimic pneumonia and present themselves with fever and pulmonary infiltrates such as pulmonary embolism and oedema, and even lung cancer.⁹

 Some of the diagnostic tests include:¹²

• Blood tests are done to confirm the presence of an infection to identify the microorganism causing the illness
• Chest X-rays are done to locate and examine the extent of inflammation in the lungs
• Pulse oximetry is done to measure the oxygen level in the blood, this is because pneumonia can hinder the lungs from moving enough oxygen into the bloodstream
• A sputum test is done using a sample of mucus or sputum taken after a deep cough for lab analysis and identification of the infection

People who are considered high-risk individuals (such as children, elderly or immunocompromised/have other medical issues) may require additional tests for confirmation and to avoid complications, some of these tests include:

• CT scans are more sensitive and give a better view of the lungs in cases of a negative chest radiograph⁹
• Arterial blood gas tests are done to test levels of oxygen in a blood sample taken from the arteries (usually the wrist). This is a more accurate test than pulse oximetry¹²
• Pleural fluid culture is done by taking a small sample of fluid from tissues surrounding the lungs for microorganism identification¹²
• Bronchoscopy is done to look into the airways of the lungs to check for any blockages¹²

Once pneumonia is diagnosed, treatment can be commenced. This includes:^4,14

• Symptomatic treatment: staying hydrated, getting plenty of rest and using medication to treat the fever
• Antibiotics in cases of bacterial pneumonia
• Antiviral drugs in cases of viral pneumonia
• Pneumococcal vaccine

Prevention

Prevention of pneumonia can be done through multiple measures, including:¹⁵

• Pneumococcal vaccine
• Washing hands regularly
• Avoid smoking
• Maintaining good health habits e.g. exercise, diet
• Managing existing health conditions such as diabetes, asthma or COPD

Summary

Influenza and pneumonia go hand in hand, while influenza is due to a viral cause, pneumonia can be either viral or bacterial and even present itself in an influenza infection. Both these illnesses can develop into severe cases and cause death and morbidity. Although the treatment is simple, it is important to have the proper diagnosis and treatment for the case at hand, more so in patients who are at high risk.