A new study published in the Journal of Infectious Diseases confirms that HIV dual infection and HIV reinfection are common.
Researchers at University of California in San Diego and colleagues used new sequencing technology and phylogenetic analyses to determine the incidence and prevalence of dual infection by more than one strain of HIV in the same individual. 
Dual infection can include either:
Co-infection, in which infection with a second viral strain occurred simultaneously or very soon after primary infection; or
Superinfection, in which a second viral strain is acquired after immune responses to the first strain have been established.
These dual infections can either be intra-subtype, where both strains are from the same viral clade, or inter-subtype, where the dual infections are established by different clades. Dual infection has previously been associated with faster rates of CD4 count decline more rapid rises in viral load and more rapid disease progression. 
The recent development of next generation sequencing technology enables the more accurate and efficient detection of dual infection, with the ability to detect circulating minority variants that are as low as 0.25% of the viral population. This could help reveal valuable information about the impact of dual infection on disease progression as well as potential correlates of protection against superinfection.
In this longitudinal study, plasma samples were collected at regular time points between January 1998 and January 2007 from 118 treatment-naïve participants with recent HIV infection in the San Diego Primary Infection Cohort. Those patients that initiated ART were followed until their viral load became undetectable (<50 copies/mL). The median time from the estimated date of infection to the baseline time point in these subjects was 71 days (IQR: 70–133).
Seven cases of co-infection were detected at baseline using this technique. The median time from the estimated date of infection for the detection of co-infection was 2.8 months (IQR: 2.3–3.2). This result translated to a coinfection prevalence of 5.9% (95% CI, 2.4–11.8%). Over a total of 201 person-years of follow up (PYFU), 10 subjects were found to have acquired superinfection. The incidence of superinfection was 4.96 per 100 PY (95% CI, 2.67 – 9.22).
Full text of article available at link below –