What Is Empyema?

You're getting over pneumonia. The cough is easing, the antibiotics seem to be working — and then the fever comes back, and breathing hurts in a way it didn't before. What happened? One answer doctors look for is empyema: infected fluid — pus — collecting in the pleural space, the thin gap between the lung and the inside of the chest wall. The short video at the top of this page, about two and a quarter minutes long, explains what empyema is and what causes it, and it starts from exactly that story: empyema most often develops as a complication of pneumonia, when infection spreads from the lung into the fluid around it. This article walks through the questions patients usually ask next, in the order they usually ask them.

Isn't fluid around the lung normal?

A small amount is. The pleural space normally holds just a film of fluid that lets the lung slide smoothly as you breathe. Problems start when fluid builds up in quantity — that's a pleural effusion, covered in our guide to pleural effusion — and an empyema is the infected end of that spectrum: the fluid hasn't just accumulated, it has become pus, full of bacteria and inflammatory debris. Not every effusion that follows pneumonia becomes an empyema, but any effusion sitting next to an infected lung is watched carefully for exactly this change, because infected fluid behaves very differently from simple fluid. It tends to thicken, form pockets separated by strands of fibrin, and resist being cleared by antibiotics alone.

How would I know — what does it feel like?

The pattern in the explainer video is the classic one: the pneumonia doesn't settle, or settles and then returns. Fever that persists or comes back, chest pain that sharpens when you breathe in (pleuritic pain), breathlessness that's worse than the original illness would explain, and a general sense of going backwards instead of forwards are the usual clues. The second video on this page shows the hospital end of that pattern: a 49-year-old who'd had cough, fever and pleuritic pain for two weeks, arrived febrile and breathing fast, with a chest X-ray showing fluid on the left side — and when that fluid was sampled, it was purulent. If you're recovering from pneumonia and the fever returns or breathing gets harder rather than easier, that's not something to wait out at home; it needs same-day medical assessment. Our overview of pneumonia covers the underlying infection that starts the whole chain.

How do doctors confirm it's empyema?

Imaging comes first — a chest X-ray shows the fluid, and an ultrasound or CT scan shows whether it's one open pool or a pocketed, thickened collection, which changes the treatment plan. The confirming step is sampling the fluid itself: a needle passed through the chest wall under imaging guidance (thoracentesis) draws off a small amount, and if it comes back cloudy or frankly purulent, or tests show infection, the diagnosis is made. That sample also guides treatment, because the laboratory can identify the bacteria involved — the explainer names the two most common pneumonia bacteria, Streptococcus pneumoniae and Staphylococcus aureus, as typical culprits — and check which antibiotics they're sensitive to.

Can antibiotics alone clear it?

Usually not on their own, and this is the point patients most often underestimate. Antibiotics are essential and are always part of the treatment, but pus in a closed space is hard for antibiotics to penetrate, and an empyema left undrained tends to organise: the fluid thickens and a peel of fibrin forms over the lung, trapping it so it can't fully expand. So the standard approach is antibiotics plus drainage. Drainage usually means a tube placed into the pleural space — the procedure is covered in our guide to chest tubes — left in place until the infection and fluid clear. In some cases the team adds medicines through the drain to help break down the pockets, and keeping the space sealed shut afterwards is a related but different procedure, described in our article on pleurodesis.

When is surgery needed?

If drainage and antibiotics don't clear the collection, or the empyema has already organised into a thick rind around the lung, surgery enters the picture. The operation is called decortication: the surgeon removes that fibrous peel so the lung can re-expand and fill the chest again. It's sometimes done through keyhole chest surgery — the same family of approaches used for a collapsed lung — and sometimes through an open incision, depending on how advanced the organisation is. The case video linked in this article, about a minute and a half long, is a decortication performed for exactly this problem. Whether you need it, and when, is a judgment your respiratory and surgical teams make from your scans and your response to drainage — earlier referral tends to mean a smaller operation, which is one more reason a returning fever after pneumonia deserves prompt attention rather than patience.

References & further reading

• MedlinePlus Medical Encyclopedia — Empyema: https://medlineplus.gov/ency/article/000123.htm
• MedlinePlus — Pneumonia: https://medlineplus.gov/pneumonia.html
• MedlinePlus Medical Encyclopedia — Pleural effusion: https://medlineplus.gov/ency/article/000086.htm

MedicalVideos.com has published trusted medical videos since 2007. The site was founded by Dr. Mohamed Ibrahim, MD, PhD — physician-scientist.

Frequently Asked Questions

What is the difference between a pleural effusion and an empyema?

A pleural effusion is any build-up of fluid in the space around the lung. An empyema is a specific kind of effusion: the fluid is infected and has become pus. Every empyema is an effusion, but most effusions are not empyemas.

What causes empyema?

Most often, pneumonia. Infection in the lung spreads into the pleural fluid next to it. It can also follow chest surgery, chest injury, or infection spreading from elsewhere in the body.

Does empyema always need a chest drain?

In practice, drainage is a core part of treatment alongside antibiotics, because antibiotics alone penetrate pus in a closed space poorly. The exact drainage method depends on how thick and pocketed the fluid is.

What is decortication?

It is an operation to peel away the thickened, fibrous rind that an organised empyema can form over the lung, so the lung can expand fully again. Surgeons consider it when drainage and antibiotics haven't cleared the infection.

When should I seek help urgently?

If you're being treated for pneumonia and the fever returns or persists, chest pain on breathing develops, or breathlessness worsens, seek same-day medical assessment — these are the classic signs that fluid around the lung may have become infected.

This article is for general education only and is not medical advice. It does not replace consultation with a qualified clinician. A returning fever, chest pain on breathing, or worsening breathlessness during or after pneumonia needs prompt medical assessment.

Dr. Mohamed Ibrahim, MD, PhD

Physician-scientist · Founder, MedicalVideos.com

Dr. Ibrahim founded MedicalVideos.com in 2007 to make medical and surgical education freely accessible to students, clinicians, and patients.

Last reviewed: 11/08/26