The prevalence of NAFLD (nonalcoholic fatty liver disease) in HIV-infected patients is higher than that in general population, but the causes of morbidity and pathogenesis have not been fully explored. The investigators are planning to consecutively enroll 400 cases HIV-positive outpatients, and to detect NAFLD by ultrasound. The fecal and blood samples were also collected to explore the mechanism of NAFLD. The investigators aimed to determine the prevalence and risk factors of NAFLD in HIV infected patients.

Inclusion Criteria:

• Age 18~70 y;
• HIV-positive patients;
• written the informed consent

Exclusion Criteria:

• coinfected with HBV, HCV;
• secondary causes of fatty liver (eg, consumption of amiodarone and tamoxifen) and decompensated liver disease;
• significant alcohol consumption (>20 g per day for man, >10 g per day for woman);
• received antibiotics in preceding two months;
• autoimmune disease;
• severe heart, lung, kidney, brain, blood diseases or other important systemic diseases;
• pregnant or lactating women

HIV-infected outpatients who was not coinfected with other form of viral hepatitis or drug induced liver disease, some severe systematic disease