Pneumonia: Classification

by Jeremy Brown, PhD

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    00:02 So pneumonia is classified into different types. The first, and the most important and the subject of most of this talk today is community acquired pneumonia, and that is what it says in his name, is a pneumonia that is acquired when you're living at home and not in hospital or anything else. So it's the normal standard pneumonia that you pick up in your everyday life. There is a subcategory of community acquired pneumonia called healthcare associated pneumonia, which has been defined recently in America but probably is not relevant in Europe, and I am not going to discuss that in any more detail today. That is a pneumonia that occurs in people who are in long-term care facilities, nursing homes, etc. but in fact in Europe there is probably not that much difference from normal community acquired pneumonia, and therefore we group it with community acquired pneumonia. The other important forms of pneumonia are hospital acquired which as it says is a pneumonia that you develop when you're in hospital, so you're admitted to hospital for another reason, say you are having an operation, and then after the operation, you develop pneumonia. That would be a hospital acquired pneumonia. It's also those patients who have been in hospitals recently and then come back in with the pneumonia because the organisms that are causing that pneumonia have probably been acquired whilst they are in hospital previously, they are also defined as hospital acquired pneumonia. A third form of pneumonia is ventilator acquired.

    01:27 That's basically a subtype type of hospital acquired pneumonia but it means this is pneumonia in patients who are on intensive care unit being ventilated with endotracheal tube inserted, and they are susceptible to pneumonia because the ET tube, the endotracheal tube, bypasses quite a lot of the normal immune mechanisms for preventing infection. And the last category, immunocompromised host. These are patients who have a very severe defect to their immune system and that allows a range of unusual organisms, bacteria, viruses, and fungi to cause the pneumonia. So the chance of having a pneumonia through unusual reason is much higher in these patients. But we are talking about patients who have severe immunocompromised state, so those who have chemotherapy for cancer, those with HIV infection, with poor CD4 counts, those who had transplantation of their marrow, or kidney or their lung, etc., so patients with very severe immune defects.

    02:31 So who gets pneumonia? Well, there's an easy answer to that question, that is, absolutely everybody could get pneumonia. It's not uncommon in young people, but it is particularly common in two age groups: the very young, the under 5s and as I mentioned before it’s the commonest cause of deaths across the developing world in the under 5s, and the elderly and there's an almost exponential increase in the chance of developing pneumonia after the age of 65.

    02:58 So it ends up that the chance of developing pneumonia in somebody who is very old, over 85, is about 5% a year. The risk factors for pneumonia also, as well as age, include previous influenza or other viral infections, because as I mentioned in the influenza lecture, a viral infection of the respiratory tract affects the immune response to bacteria, and allows bacterial infections to develop as a consequence of the viral infection, so secondary bacterial pneumonia is after influenza are very common and that's the major way by which death is caused during the pandemic, or has been in the past. For example the post-World War I pandemic which killed 20 million people, most people died of pneumococcus and staphylococcus pneumonia after having the influenza virus infection. Other people who are more susceptible to pneumonia are alcoholics, people with liver cirrhosis, and that affects the ability of the immune system to fight bacteria. Smokers, allows the bacteria to establish infection in the lungs more readily; actually having had one episode of pneumonia makes you two or three times more likely to have another episode, it marks you out as somebody who is susceptible to pneumonia. And then, patients with chronic disease. Chronic lung disease, COPD for example; chronic neurological disease, dementia, previous stroke, etc..

    04:15 Any renal impairments or cardiac failure. These are all reasons why, these all will increase the chance of getting community acquired pneumonia. Now, if you have hospital acquired pneumonia you need to be in hospital, so if you are hospitalized for one a reason, you are at risk of hospital acquired pneumonia, and if you are ventilated then you are at risk of ventilator acquired pneumonia. And the risk of that is about 1% per day that you are ventilated. And then of course, the patients who have immunosuppressed for their treatment for their cancer or because they've had a lung transplantation etc. Those will be at risk of pneumonia of the immunosuppressed patient.

    About the Lecture

    The lecture Pneumonia: Classification by Jeremy Brown, PhD is from the course Infections of the Respiratory Tract.

    Included Quiz Questions

    1. High socioeconomic status.
    2. Recent influenza infection.
    3. Smoking.
    4. HIV infection.
    1. Pneumonia acquired 48 hours after admission for another reason
    2. Pneumonia acquired out of the hospital
    3. Healthcare associated pneumonia
    4. Pneumonia associated with the use of ventilators in the hospital
    5. Pneumonia associated with chemotherapy in the hospital
    1. All the options are risk factors for pneumonia.
    2. Previous episodes of pneumonia.
    3. Alcohol consumption and smoking.
    4. History of viral infections.
    5. People who are not vaccinated for influenza virus.

    Author of lecture Pneumonia: Classification

     Jeremy Brown, PhD

    Jeremy Brown, PhD

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