Septic arthritis
Acute bacterial infection of joints is quite rare in HIV-infected patients and when it does occur, it is more likely in people who inject drugs. As is the case in the general population, Staphylococcus and Streptococcus are the commonest organisms found (3). Early diagnosis with diagnostic aspiration revealing purulent synovial fluid should be promptly followed by orthopaedic referral and joint washout. Repeat joint washout may be required, in addition to intravenous antibiotics, which are usually followed by oral antibiotic therapy. As antibiotics are usually required for several weeks, the specific diagnosis that aspiration, culture and sensitivity testing can yield is critically important. Other causes of septic arthritis include gonococcal septic arthritis, though a recent review noted this to be rare in the setting of HIV infection (37).
Pyomyositis
Bacterial infections of muscles have been rarely reported in HIV-infected patients in the last few years. As is typical for the disease in any population, pyomyositis may present as a single (or multiple) abscess(es), either spontaneously or after trauma (eg. intramuscular injection). Gram positive organisms especially Staphylococcus aureus are the most common bacteria found. The disease course may be indolent at first but later present with increasing symptoms of infection, such as fever, pain and swelling. Imaging and surgical drainage are both diagnostically and therapeutically essential (38). Occasionally the pyomyositis may be part of an immune reconstitution inflammatory syndrome associated with Mycobacterium tuberculosis infection (39).
Osteomyelitis
Osteomyelitis in patients with HIV infection may be acute or chronic and be the result of haematogenous or contiguous spread. Again, Staphylococcus aureus is the most common organism to cause the disease though there are many reports of other pathogens, such as Salmonella, Nocardia and fungi such as Cryptococcus and Candida (40). In some settings tuberculous osteomyelitis has been common and it may particularly involve the spine causing bone, joint and sometimes serious neurological pathology (38).
In a staphylococcal infection, a positive blood culture sometimes identifies the organism causing the bone pain, however a targeted bone biopsy might be necessary. In chronic osteomyelitis, surgery is frequently needed to remove a piece of dead bone (a sequestrum) that forms the nidus of the infection and this creates an excellent opportunity for cultures to be undertaken. This procedure is best performed when the patient is not on antibiotics. As with non-HIV-infected patients, chronic osteomyelitis may require a short course of intravenous antibiotics followed by weeks to months of oral antibiotics. In contrast, acute osteomyelitis may not need surgical debridement but respond to few weeks of targeted intravenous antibiotics followed by a short oral tail. Atypical organisms (eg. fungi, mycobacteria) may necessitate much longer durations of therapy (41).