One in five people with recent HIV infection in Spain have X4/R5 mixed tropic virus

Simon Collins, HIV i-Base

A retrospective Spanish database study reported very high levels of X4 infections in an anonymised population based surveillance study.

The study presented by Rocio Sierra-Enguita from Hospital Carlos III in Madrid, of 1031 people diagnosed from 1997 – 2012 with primary HIV infection (PHI), reported that approximately 23% of samples since 2010 indicated X4-tropism. This was significantly increased from levels at approximately 11% for the years prior to 2003, (p=0.03). Non-B subtypes were not detected from 1997-2000 but were at 18% from 2010-2012, p=0.003).

The median time of diagnosis since infection was estimated at 5 months (IQR 5 to 10), with median CD4 and viral load at diagnosis of 533 cells/mm3 (IQR 408 – 737) and 4.5 log copies/mL (IQR 4.1 – 5.0), respectively. Approximately 13% of PHI patients were non-B subtype and 84% were MSM.

Unfortunately, the anonymity of study design limited the ability to look for risk factors that might explain the increases.


Sierra-Enguita R et al. X4 tropic viruses are on the rise in recent HIV-1 seroconverters. International Workshop on HIV and Hepatitis Virus Drug Resistance and Curative Strategies, 4-8 June 2013, Toronto. Oral abstract 14. (abstract book) (PDF slides)

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