Hello
It is very difficult to establish any diagnosis when patient it taking antiretroviral treatment .
It become more important particularly when CD+4 cell counts is less than 70 /mictoL.
As you stated that , your sister in in the hospital and still her CD+4 is dramatically low , may be due to these reason in the presence of fever :
1 Patients with CD+4 Tcell counts less than 200 /micro Lare at the risk of infection with PNEUMOCYSTITIS JIROVECI. Patients dysponea , fever and non-productive cough.
Blood also shows increase level of lactate dehydrogenase.
2 Another reason of such low count may be due to
CYTOMEGALOVIRUS DISEASE . Diagnosis can be confirmed by an OPHTHALMOLOGIST for
retinitis .
3
Mycobacterium avium intracellulare , one indication is counts less than 70 CD+4
T cell.
Since count is very less so in HIV infected there develop "
OPPORTUNISTIC INFECTION " , so as I mentioned fever may be due to above mentioned reason .
Hope this will help you in framing the future plan of treatment .
Good luck .