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Geography

Tropical pyomyositis occurs most frequently in tropical Africa and New Guinea, but is also seen in Malaysia, Indonesia, Hawaii and other Pacific Islands, Jamaica and elsewhere in the West Indies, Ecuador, Brazil and other South American countries, and southern nontropical Africa. In some areas, pyomyositis is surprisingly common; for example, there were over 800 cases in one report alone from East Africa; by comparison, similar infections are distinctly uncommon in temperate climates, even when those occurring in immigrants are included.

Epidemiology

The data from many of the published series from different parts of the tropics are contradictory, although clearly describing the same entity. In some areas, the frequency is increasing, whereas in others these abscesses are becoming less common. Some series have a predominance of patients in the third and fourth decades; in others, the patients are below the age of 20 and the abscesses occur in school children as well as young laborers. In all reports, the abscesses in adults are more common in men than women.

Attempts to relate the origin to geography and climate are not convincing; for example, 25 patients with 32 abscesses were seen in 12 months at one hospital in Swaziland, a country where there is a temperate climate and the altitude varies from 225 m to nearly 2,000 m, with an average of 1,400 m. Cases have been reported from Thailand, which has a completely different climate. Nevertheless, pyomyositis is 20 times more common in the tropical forests of Ecuador than high in the Andes, but the high mountains do not provide complete protection for those who live there. Although cases are reported in Caucasians and Indians, including some who live in and have never left Ecuador, the overwhelming majority are indigenous, ethnic patients: in this group pyomyositis occurs twice as often as would be expected from their numbers in the surrounding population. A seasonal variation has been noted in Uganda, where in the 1970's and 1980's there were 250-300 patients seen at the Mulago hospital, Kampala, every year. It does seem to be more common in the rainy season. The vast majority of patients are from rural areas and are in agricultural occupations. There are a surprising number of children infected, and the male/female ratio is even until after childhood. It is possible that the adult male preponderance reflects only the common hospital attendance pattern. This difference may disappear as medical services become more available and women are more willing to accept them.

The infection affects skeletal muscle and the abscesses are intramuscular. In some reports they occur predominately in the lower limbs, particularly the thigh and gluteal regions; in others they are more common in the shoulder region, the upper limbs, and the abdominal and vertebral muscles, with occasional cases in the internal pelvic muscles. For example, in one series of 58 patients in Uganda, 30 were men and 28 were women. The patients' ages were from 4 to 65 years. There were multiple lesions in 18 patients; true pus-forming abscesses were found in 42 patients, and a more diffuse edematous infiltration in the other 16. About half the infected sites were in the chest or abdominal muscles.

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Copyright: Palmer and Reeder