Molecular epidemiology studies of HIV diversity around the world are of pivotal importance to the containment of an HIV/AIDS pandemic. An increasing body of evidence suggests that differences of HIV types, groups and subtypes influence on their biological characteristics and on the impact of clinical intervention strategies . This is particularly true for the effective design of HIV vaccine candidates, where one should know the genetic variants of the virus that circulate in specific targeted regions . HIV-1 group M, the pandemic group of the virus, is divided into nine distinct subtypes (A–D, F–H, J and K) and over 30 intersubtypic circulating recombinant forms [3,4]. In a report recently published in AIDS, Hemelaar and colleagues have analyzed the most updated global and regional distribution of HIV-1 genetic strains, comprising over 20 000 strains isolated from 2000–2004 in 70 countries representing all continents . Data were compiled according to the relative contributions of investigators from those countries, and our group was one of the Brazilian contributors.
Our group is mostly interested in the spread of HIV-1 subtype C, which is still a minor variant in Brazil, but highly concentrated to the southernmost part of the country [6–9]. Even although a large number of the contributed HIV sequences by our group derived from a nationwide HIV diversity survey , that survey was highly represented by samples from the southernmost states of Brazil, notably from Rio Grande do Sul and Paraná. Additional sequences were also obtained from our HIV diversity studies conducted in southern Brazil [6,8,9]. Rio Grande do Sul concentrates most of subtype C infections in Brazil, but it harbored only 10% of all Brazilian HIV infections in 2004 . In addition, subtype C infections outside southern and southeastern Brazil and in other Latin American countries are only anecdotal.
In order to evaluate potential geographical and convenience sampling biases in the estimates of Latin America proposed in , we have estimated subtype C infections in Brazil based on the relative contributions of cases from each state of the country where subtype C prevalence is significant (over 1%) in 2004 . We have also used data from the most recent HIV molecular epidemiology nationwide  and local surveys [8,9]. The five Brazilian states where subtype C circulate in proportions above 1% harbors over 63% of HIV/AIDS cases in the country (Table 1). However, by using the estimates of subtype C infections in those states, we find it to represent less than 9% of the total HIV infections in the country. As subtype C infections have so far been only sporadically reported in other Latin American countries, and considering that Brazil harbors 35% of the HIV infections in Latin America , the total contribution of subtype C to the epidemic in that continent can be as low as 3.1%. This is less than one quarter of the 12.6% reported by Hemelaar et al. .
In this report, we were able to verify the effect of potential biases in the estimate of subtype C prevalence in Latin America. We anticipate that similar geographical concentrations and convenient samplings, mostly related to the use of HIV pol genomic regions sequenced for drug resistance surveys, may have taken place in other parts of the world, where restricted investigators conduct HIV molecular surveys. Although the monitoring of HIV epidemiology is of extreme importance to rational policy contention strategies, any results relating to HIV subtype prevalence should be taken with caution and more prospective, unbiased designed surveys should be carried out.
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