Low grade Infection

Benjamin Kadler, Saurabh Mehta  & Lennard Funk

What is a 'low' grade infection?

The usual bacterial infections have symptoms of severe pain, swelling, redness, high fevers, pus and generally feeling unwell. These are the recognised infections. They are obvious.

A low grade infection usually follows surgery or other interventions, such as joint injections. They are less common and more difficult to recognise and diagnose. The symptoms are usually persistant aching pain after surgery which does not respond to the usual treatments. The joint is often very stiff and extremely painful. There is no fever, sweats or general ill-health. Blood tests, temperature and x-rays are normal.

The organisms that cause this are ones that live on your skin and in your body normally. The stress of the intervention causes them to proliferate and behave abnormally causing a low grade infection. The most common organism is Proprionibacterium Acnes (P. acnes).

What is P. acnes?

P. acnes is short for Propionibacterium acnes. It is a type of bacteria that usually lives in the pores of your skin. Most of the time it doesn’t cause any harm but, when the skin is cut during surgery, the bacteria can travel inside and infect parts of the body. The shoulder has a lot of this type of bacteria living there so patients having shoulder operations are prone to this type of infection. Infection with P. acnes is important because it is uncommon and often difficult to diagnose. 

Who is at risk?

Infection with P. acnes after shoulder surgery is RARE and depends on which operation you have had. It occurs, on average, in less than 2% of patients. P. acnes infection can happen to anyone, however, some of the risk factors are:
Male gender
Younger people
Operations involving an implant
Previous shoulder surgery
Trauma to your shoulder being the reason for your surgery

How do you suspect if you have it?

P. acnes infection does not show itself like other post-surgical infections. The common infection signs of fever, swelling and redness at the surgical site are not present. Blood tests for infection (CRP and ESR) are often normal. 
P. acnes is SLOW GROWING so symptoms might start 3 months or even 1 or 2 years after your operation. 

The most important way to diagnosis it is to have a high index of suspicion in the following instances:
- A stiff or tight shoulder for MONTHS after your operation that is not responding to physiotherapy and injections?
- Dull, aching pain in the shoulder that won’t go away months down the line
- Persistent swelling of the shoulder

What will happen next?

- First of all the doctor will examine your shoulder and then you might have a blood tests, x-rays and/or an MRI scan  - X-rays may show loosening of the implant
  - MRI scan may often show inflammation at the surgical site
- Often samples from your shoulder need to be sent to the laboratory to try find the P. acnes organism. This involves specialist ‘extended cultures on enriched media’
- If the doctors find that your shoulder is infected the treatments available are antibiotics and possibly another operation to remove the infection.

For more information, please see the Education Section and also Youtube video:

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