Bacterial Pneumonia

Published: March 10, 2016
Last reviewed: June 15, 2017

What is bacterial pneumonia?

Bacterial pneumonia is an infection of the lung’s air sacs (parenchyma) [5]. It is the most common type of pneumonia, which most commonly occurs in individuals with underlying diseases.

Main symptoms include coughing up mucus, shortness of breath and high fever. Diagnosis can be made from sputum and blood culture and X-ray image. Treatment is by antibiotics; if left untreated, bacterial pneumonia can be deadly.

Symptoms and Signs

Early symptoms can include sudden high fever or hypothermia (up to 105 °F or 40.5 °C or lower than 95 °F or 35 °C), shaking chills, difficulty breathing (dyspnea), coughing up yellow, green or rusty sputum (occasionally with blood in it) and severe fatigue, a headache and diarrhea [5].

Late symptoms (after few days) include sharp, stabbing chest pain triggered by deep breathing (due to pleurisy) and persistent dry cough and fatigue that slowly wear off.


  • Increased breathing frequency (tachypnea) and heart rate (tachycardia)
  • Paleness, excessive sweating, clammy skin
  • Crackling sounds, decreased breathing sounds or wheezing detected by auscultation (listening of the lungs by the stethoscope).
  • Dull sounds during percussion (tapping the chest by the fingers)
  • Bluish discoloration around the mouth (cyanosis) and confusion (in severe pneumonia)
  • White spots on the nails (white nail syndrome or leukonychia)

References: [4,5,13,14,24]


The most common causes of bacterial pneumonia:

  • In adults: Streptococcus pneumoniae (pneumococcus) [5]
  • In small children: Haemophilus influenzae B (HIB) [2,3]
  • In elderly with an underlying heart diseaseMoraxella catarrhalis [9]
  • In hospitalized individuals: Staphylococcus aureus [5]
  • After aspiration of vomit: anaerobic bacteria: Klebsiella [5]

Causes of severe bacterial pneumonia [5]:

Staphylococcus aureus causes pneumonia mainly in hospitalized individuals, especially in those on mechanical ventilation, in infants and young children, those with chronic lung diseases or recent influenza and in intravenous drug users [2,5,6].

Methicillin-resistant Staphylococcus aureus (MRSA) can cause life-threatening pneumonia [20].

Klebsiella pneumoniae that produces the enzyme carbapenemaze (KPC) is resistant to a class of broad-spectrum antibiotics called carbapenems (imipenem, meropenem) and also penicillin and cephalosporins; it can cause “resistance pneumonia,” almost exclusively in hospitalized individuals with impaired immunity [21]. It has a high mortality rate [5]. A typical symptom is coughing up red currant jelly phlegm [5].

Streptococcus pyogenes (group A streptococcus or GAS) can cause invasive necrotizing pneumonia [7].

Pseudomonas aeruginosa is a common cause of pneumonia in individuals with cystic fibrosis and those on mechanical ventilation. It can have a fulminant course; a typical symptom is a green sputum [5].

Mycobacterium avium complex (MAC) is a group of bacteria that causes pneumonia, mostly in individuals with HIV/AIDS [11] or a “hot tub lung” [10].

Other bacteria that can cause pneumonia: Acinetobacter, Actinomyces, Enterobacter, Enterococcus, Escherichia coli, Meningococcus, Neisseria gonorrhoeae, Nocardia, Salmonella typhi, Serratia [5].

Atypical bacteria, such as Mycoplasma, Chlamydophila and Legionella, can cause atypical pneumonia.

Secondary Bacterial Pneumonia

Secondary bacterial pneumonia occurs as a complication of an acute viral infection, such as influenza or infection by Respiratory syncytial virus (RSV), Adenovirus or Rhinovirus [5,20] or acute bacterial infection, such as whooping cough [22].

Is bacterial pneumonia contagious?

Bacteria that cause pneumonia spread by droplet infection (by coughing, sneezing or kissing) from the infected persons even when they have no symptoms. Individuals with impaired immunity can get pneumonia by inhaling pneumococci or other bacteria that normally live in the mouth, nose or throat. Intravenous drug users can get pneumonia by allowing normal skin bacteria, like staphylococci, to enter the blood and then the lungs.

Bacterial pneumonia usually occurs in individuals with risk factors, such as influenza, asthma, chronic obstructive pulmonary disease (COPD), cystic fibrosis, smoking, alcoholism, heart failure, previous surgery, or impaired immunity (HIV/AIDS, steroid treatment).

If you are otherwise healthy and you are in close contact with someone who has bacterial pneumonia, you may catch bacteria from the person, but this may not necessary result in pneumonia.

Bacterial pneumonia is more common in winter and early spring [12]. Incubation period–the time from exposure to bacteria to onset of symptoms–is 1-3 days [8]. It is not known for how long is the infected person contagious [13].

You can get pneumonia more than once, even if you have been vaccinated because there are more than 90 known strains of pneumococcus bacteria, but vaccine protects only against 23 of them.


Bacteria trigger lung inflammation with fluid accumulation in the air sacs (alveoli), which hampers oxygen exchange between the lungs and blood.


  • Blood tests:
    • Blood culture can reveal the causing bacteria
    • White blood cells (WBC): increased number of white blood cells (leukocytosis)
  • A sputum culture can reveal bacteria.
  • Pulse oximetry can roughly determine blood oxygen concentration and thus the severity of pneumonia.
  • X-ray:
    • Lobar pneumonia, which affects a large part of one, or rarely 2 or more lung lobes, presents with one or more large continuous dense white shadows (consolidation)
    • Bronchopneumonia, which affects small parts (lobules) of the tissue, presents with many scattered small white patches, usually in both lungs
  • Rapid urine antigen test can reveal the bacterium Streptococcus pneumoniae.
  • Reference: [15]

Differential Diagnosis

Health conditions similar to bacterial pneumonia:

Chart 1. Bacterial vs Viral Pneumonia



Common causes Streptococcus pneumoniae Influenza virus
Cough Yellow, green or rusty sputum Clear or yellow sputum
Fever High (>104 °F or 40 °C) Moderate: ~100 °F or 38 °C
Shortness of breath Common Occasional
X-ray (common pattern) Lobar pneumonia Bronchopneumonia
Treatment Antibiotics Antivirals or no drugs

NOTE: There is no single symptom or X-ray pattern that would allow a reliable differentiation between bacterial and viral pneumonia.


At Home

  • Rest in bed as long as you have a high fever but try to get off the bed as soon as you feel better and walk around; avoid any heavy exertion, though.
  • Some health professionals recommend breathing exercises: every hour, when sitting or standing, take few deep breaths and then cough out any mucus thoroughly [24]. It may help you to clear mucus if you inhale steam from the boiling water before coughing.
  • Drink enough fluid to prevent dehydration.


The initial treatment for otherwise healthy individuals, before the results of the blood and sputum culture are known, can include azithromycin or erythromycin [18].

When the causing bacterium is identified, the following antibiotics can be used:

  • Streptococcus pneumoniae: penicillin
  • Haemophilus influenzae: amoxicillin
  • Staphylococcus aureus: penicillin
  • Methicillin-resistant Staphylococcus aureus (MRSA): vancomycin
  • Klebsiella pneumoniae carbapenemase (KPC): colistin [21]
  • References: [3,13,18]

In order to kill bacteria efficiently and thus prevent pneumonia from recurring, you should take antibiotics for as long as the doctor has prescribed them to you, even if you feel better after few days.

In Hospital

For severe pneumonia, intravenous antibiotics, bronchodilators (albuterol via a nebulizer), oxygen mask or mechanical ventilation are often required [16].

It is not clear, if corticosteroids (prednisone) are beneficial in treatment of bacterial pneumonia [19].

Recovery Time and Prognosis

With appropriate treatment, you can expect an obvious improvement with a drop of the body temperature within 48-72 hours [3]. After that, you can still have dry cough or hear some crackling sounds during breathing, and you can expect to recover completely within 1-3 weeks. Elderly and those with chronic diseases may experience fatigue, coughing up sputum and shortness of breath for more than 6 weeks or even few months after starting antibiotic treatment [23,24]. Untreated or ineffectively treated bacterial pneumonia can be life-threatening [17].


Complications of bacterial pneumonia can include dilatation of bronchi (bronchiectasis), collection of pus in the lung tissue (abscess) or pleural space (empyema), blood infection (sepsis), meningitis, middle ear infection (otitis media), acute respiratory distress syndrome (ARDS), another infection or death [3,13].

2 Responses to Bacterial Pneumonia

  1. Scott Gribble says:

    My nephew is 65 years old, long history of COPD. He was hospitalized 2 weeks ago, H1/N1 flu virus, diagnosed several days later with pneumonia and within the last several days with MRSA in his lungs. The hospital appears to be leaning towards releasing him in a few days. Since we are roommates, I’m concerned with the possibility of becoming infected. It is my understanding the MRSA infection can be controlled but not eliminated. Since my nephew is prone to long coughing fits from COPD, could he still potentially be contagious at some point after he is released from the hospital?

    • Jan Modric says:

      Scott, I cannot give a reliable answer. MRSA is resistant to classical antibiotics, but it can be completely treated with other antibiotics, not just controlled. Someone with COPD may be at increased risk to get MRSA infection again, though. If you are healthy and you did not have pneumonia before, it is less likely you will contract MRSA from him or even if you do, it is not very likely that you will develop pneumonia. Bacterial pneumonia usually develops in lungs that are affected by some other disease, for example by influenza virus. Usually, everyone who had MRSA and was treated needs to be checked to see if the infection has recurred, so I assume, your nephew will be instructed to have tests for MRSA soon after he leaves the hospital. I strongly encourage you to have a short discussion about this with the doctors who treated him.

Load more comments
Show less

Leave a Reply

Your email address will not be published. Required fields are marked *