Pneumonia: Classification

00:00 So, pneumonia is classified into different types.

00:04 The first -- the most important and the subject of most of this talk today is community acquired pneumonia.

00:11 And that is what it says in its name is a pneumonia that is acquired when you're living at home and not in hospital or anything else.

00:18 So it's the normal standard pneumonia that you pick up in your everyday life.

00:23 The other important forms of pneumonia are hospital acquired which as it says is a pneumonia that you develop when you're in hospital.

00:31 So you're admitted to hospital for another reason, say you're having an operation and then after the operation you develop a pneumonia.

00:38 That will be a hospital acquired pneumonia.

00:40 A third form of pneumonia is ventilator acquired.

00:43 That's basically a subtype of hospital acquired pneumonia.

00:46 But it means this is pneumonia in patients who are on intensive care unit being ventilated.

00:52 And they are susceptible to pneumonia because the ET tube, the endotracheal tube bypasses quite a lot of the normal immune mechanisms preventing infection.

01:02 And the last category, the immunocompromised host.

01:05 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 is much higher in these patients.

01:24 But we're talking about patients who have severe immunocompromised state.

01:27 So those who've had chemotherapy for cancer, those with HIV infection, with poor CD4 counts, those who had transplantation with their marrow or their kidney or their lung, etc.

01:38 So patients really with very severe immune defects.

01:42 So, who gets pneumonia? Well, there's an easy answer for that question.

01:46 That is absolutely everybody could get pneumonia. It's not uncommon in young people.

01:50 But, it is particularly common in two age groups. The very young, the under-fives.

01:55 And as I mentioned before, it's the commonest cause of death across the developing world in the under-fives and the elderly.

02:03 And there's an almost exponential increase in the chance of developing pneumonia after the age of 65.

02:08 So, it ends up that the chance of developing pneumonia in somebody who's very old over 85 is about 5% a year.

02:16 The risk factors for pneumonia also as well as age include previous influenza or other viral infections.

02:23 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.

02:35 So secondary bacterial pneumonias after influenza are very common.

02:39 And that's the major way by which death is caused during the pandemics or has been in the past.

02:45 For example the post-World War I pandemic which killed 20 million people.

02:48 Most people died of pneumococcal and Staphylococcus pneumonia after having the influenza virus infection.

02:55 Other people who are more susceptible to pneumonia are alcoholics or people with liver cirrhosis cuz that affects the ability of the immune system to fight bacteria.

03:05 Smokers, allows the bacteria to establish infection in the lungs more readily.

03:09 Actually having had one episode of pneumonia makes you two or three times more likely to have another episode.

03:15 It marks you out as somebody who's susceptible to pneumonia.

03:17 And then patients with chronic disease, chronic lung disease, COPD for example, chronic neurological disease, dementia, previous stroke, etc.

03:26 Any renal impairment or cardiac failure.

03:30 These are all reasons why -- these all increase the chance of getting community acquired pneumonia.

03:35 Now, if you have hospital acquired pneumonia, you need to be in hospitals.

03:40 So if you're hospitalized for a reason, then you're at risk of hospital acquired pneumonia.

03:44 And if you're ventilated, then you're at risk of ventilator acquired pneumonia.

03:48 And the risk of that is about 1% per day that you are ventilated.

03:51 And then of course the patients who have immunosuppressed for their treatment for their cancer or because they've had a lung transplantation, etc.

04:01 Those will be at risk of pneumonia of the immunosuppressed patient.