@article{portela_simpson_1997,  title={Markers, Cofactors and Staging Systems in the Study of HIV Disease Progression: A Review},  volume={92},  ISSN={0074-0276},  url={https://doi.org/10.1590/S0074-02761997000400001},  DOI={10.1590/S0074-02761997000400001},  number={4},  journal={Memórias do Instituto Oswaldo Cruz},  publisher={Instituto Oswaldo Cruz, Ministério da Saúde},  author={Portela, MC and Simpson, KN},  year={1997},  month={Jul},  pages={437–457} }