Bacteraemia means bacterial infection of the blood. This is common in people with HIV because bacterial infections in organs such as the lungs or gut can spread into the bloodstream. Moreover, injecting drug users may inadvertently inject bacteria into their blood through unsterile injecting equipment, and medical procedures can either directly lead to infection (for example, through insertion of central venous lines) or indirectly (for example, drugs that cause the neutrophil count to fall).

Septic arthritis in HIV-infected haemophiliacs has been linked to bacterial infections. Antibiotics are usually sufficient to resolve the arthritis.

The two most common causes of bacteraemia are Staphylococcus aureus and the so-called 'Gram negative' bacteria. Different bacteria are treated with different antibiotics. Catheter-associated infections may initially be treated with antibiotics leaving the catheter in place, but if the individual is acutely ill or has persistent fever or bacteraemia it is usually necessary to remove the catheter.

An antibiotic-resistant form of S. aureus, known as methicillin-resistant S. aureus (MRSA), has become relatively common worldwide. It can affect both HIV-negative and HIV-positive people, causing severe illness. It usually responds to treatment with antibiotics such as vancomycin (Vancocin) or teicoplanin (Targocid). Salmonella is also a common cause of bacteraemia worldwide.

As many as 50% of HIV-positive people with bacteraemia may have no symptoms. However, untreated bacterial infections can become very serious. Serious blood infection is known as septicaemia, and requires urgent treatment. Consequently, it is necessary to make a 'best guess' of the right antibiotics to give before laboratory results confirm this diagnosis.