Antiretroviral Recommendations May Influence the Rate of Transmission of Drug‐Resistant HIV Type 1

HIV/AIDS •CID 2005:41 (15 July) •227 HIV/AIDSMAJOR ARTICLE Antiretroviral Recommendations May Influence the Rate of Transmission of Drug-Resistant HIV Type 1 Carmen de Mendoza, 1 Carmen Rodriguez, 2 Jose´ Maria Eiros, 3 Javier Colomina, 4 Federico Garcia, 5 Pilar Leiva, 6 Julia´n Torre-Cisneros, 7 Jesu´s Aguero, 8 Jose´ Pedreira, 9 Isabel Viciana, 10 Ange´lica Corral, 1 Jorge del Romero, 2 Rau´l Ortiz de Lejarazu, 3 and Vincent Soriano 1 1 Service of Infectious Diseases, Hospital Carlos III, and 2 Centro Sanitario Sandoval, Madrid, 3 Service of Microbiology, Hospital Clı´nico, Valladolid, 4 Service of Microbiology, Hospital de la Ribera, Valencia, 5 Service of Microbiology, Hospital San Cecilio, Granada, 6 Service of Microbiology, Hospital Central de Asturias, Oviedo, 7 Department of Internal Medicine, Hospital Reina Sofia, Co´rdoba, 8 Service of Microbiology, Hospital Marques de Valdecilla, Santander, 9 Department of Internal Medicine, Hospital Juan Canalejo, La Corun˜a, and 10 Service of Microbiology, Hospital Virgen de la Victoria, Malaga, Spain (See the editorial commentary by Little and Smith on pages 233–5) Background. Human immunodeficiency virus (HIV) treatment guidelines have evolved, shifting from moreaggressive to more-conservative approaches. The potential impact of these shifts on the transmission of drugresistant virus is unknown. Methods. Drug-resistance genotypes were examined in all consecutive patients with recent HIV type 1 (HIV- 1) seroconversion (hereafter, “HIV-1 seroconverters”) seen at 10 Spanish hospitals since 1997. During the same period, the proportion of patients with chronic HIV-1 infection having undetectable viremia was examined, to estimate the extent and effectiveness of antiretroviral therapy. Results. A total of 141 recent HIV-1 seroconverters were identified, 67.4% of whom were men who have sex with men. The rate of primary drug-resistance mutations, by year of infection, was 33.3% for 1997, 29.4% for 1998, 20% for 1999, 14.3% for 2000, 3.4% for 2001, 15.4% for 2002, and 10.9% for 2003. On the other hand, the proportion of 8388 persons with chronic HIV-1 carriage who had an undetectable virus load was 33.4% for 1997, 34.6% for 1998, 39.7% for 1999, 47.5% for 2000, 52.9% for 2001, 39.7% for 2002, and 58.1% for 2003. A significant inverse correlation between transmission of drug-resistant HIV-1 and undetectable virus load was found ( , by Spearman’s test; ). The lowest rate of transmission of drug-resistant HIV-1 was seen inrp⫺0.955 Pp.001 2001, when relatively “aggressive” treatment guidelines were used. Transmission of drug-resistant HIV-1 increased in 2002, in parallel with a reduction in the number of patients with chronic HIV-1 carriage and undetectable virus load, reflecting the popularity of drug holidays or treatment interruptions. Conclusion. The rate of drug resistance in recent HIV-1 seroconverters inversely correlates with the proportion of chronically HIV-1–infected individuals who have undetectable virus loads in the same region, which indirectly reflects antiretroviral treatment rules at any given time. Resistance to antiretroviral drugs represents one of the major obstacles for the success of HIV-1 therapy [1]. Viruses that carry drug-resistance mutations can be transmitted to and subsequently compromise the response to antiretroviral therapy in drug-naive individ- Received 3 January 2005; accepted 19 February 2005; electronically published 31 May 2005. Reprints or correspondence: Dr. Vincent Soriano, Calle Sinesio Delgado 10, 28029 Madrid, Spain ([email protected]). Clinical Infectious Diseases 2005;41:227–32 2005 by the Infectious Diseases Society of America. All rights reserved. 1058-4838/2005/4102-0014$15.00 uals [2–4]. In Western countries, where many HIV-1– infected subjects are receiving antiretroviral therapy, an increase in the prevalence of primary drug resistance among patients with new HIV-1 seroconversion (hereafter, “HIV-1 seroconverters”) has been noticed in recent years [4–6]. Accordingly, updated guidelines recommend drug resistance testing before antiretroviral treatment is initiated for subjects with recently acquired HIV-1 infection [7, 8]. In Spain, surveillance studies conducted during the 1990s have demonstrated that the rate of genotypic resistance among drug-naive individuals with chronic HIV-1 infection decreased significantly from 1997 to Downloaded from https://academic.oup.com/cid/article/41/2/227/530871 by UNIVERSIDAD DE VALLADOLID. BIBLIOTECA user on 09 March 2021 228 •CID 2005:41 (15 July) •HIV/AIDS 2000 [9–11]. However, data from HIV-1 seroconverters are scarce, although alarming rates of primary drug resistance were reported in the late 1990s [12, 13]. In parallel, HIV-1 treatment guidelines have evolved over the past few years, shifting from more-aggressive to more-conservative approaches [14, 15]. We were interested to know the extent to which changes in antiretroviral treatment recommendations may have influenced trends in the proportion of drug-resistant viruses in newly infected individuals. For this purpose, and given the strong correlation found between plasma HIV-1 RNA level and infectiousness [16], we assumed that the proportion of patients with chronic HIV-1 infection who have detectable plasma virus loads indirectly reflects the population of potential transmitters. Thereafter, we confronted it with yearly rates of primary drug resistance among recent HIV-1 seroconverters. Specimens and information from a relatively large number of newly infected persons identified in different Spanish cities were assessed. PATIENTS AND METHODS Study Population Recent HIV-1 seroconverters. All consecutive individualswith new HIV-1 infection seen during the period of January 1997 through December 2003 at 10 different hospitals distributed across Spain (A Corun˜a, Co´rdoba, Granada, Madrid [2 hospitals], Ma´laga, Oviedo, Santander, Valencia, and Valladolid) were examined. The eligibility criteria for a given subject to be enrolled in the study were laboratory evidence of acute primary HIV-1 infection (detectable plasma HIV-1 RNA level plus negative or indeterminate HIV-1 antibody test result) or seropositivity for HIV-1 infection (reactive ELISA and Western blot results) and negative results of a previous test performed within the prior 12 months. Chronic HIV-1 carriers. During the same 7-year period, the proportion of patients with demonstrable HIV-1 infection that had lasted at least 3 years and with undetectable virus loads (!500 or !50 HIV-1 RNA copies/mL) was examined in a total of 8388 individuals. Considering that patients with chronic HIV-1 infection are regularly seen every 3 months in the outpatient clinic, only consecutive samples collected during the first trimester of each year were analyzed. The population included subjects who were drug naive and those who were receiving antiretroviral therapy. We assumed that most patients with undetectable virus loads were receiving successful antiretroviral therapy, reflecting indirectly the extent of therapy in this population. Laboratory Tests The measurement of plasma HIV-1 RNA level was performed using a branched DNA assay (Versant, versions 2.0 and 3.0; Bayer), in accordance with the manufacturer’s instructions. The lower limits of detection of the assay were 500 HIV-1 RNA copies/ mL during 1997 and 1998 and 50 HIV-1 RNA copies/mL since 1999. The CD4 + T lymphocyte count was determined by flow cytometry (Coulter) using fluorescein-labelled antibodies. Genetic sequence analyses of both HIV-1 reverse-transcrip- tase (RT) and protease genes were performed for all plasma specimens obtained from recent HIV-1 seroconverters using an automatic sequencer (ABI Prism 3100; Celera Diagnostics). For the purpose of this study, only major or primary drug-resistance mutations listed in the latest guidelines from the International AIDS Society–USA panel were recorded (http://www.iasusa.org; updated November 2004). HIV-1 subtyping was performed using pol sequences by phylogenetic analyses, as previously described [17]. Statistical Analyses Baseline characteristics of the study population were recorded as percentages or as mean . The proportion ofvalues SDs patients with drug-resistance mutations and undetectable virus loads was also recorded as a percentage. Nonparametric tests were used to compare the proportion of patients with drugresistance mutations at different time points. Spearman’s test was used to analyse the correlation between the rate of drugresistance mutations in recent HIV-1 seroconverters and the proportion of potential transmitters at different time points. All reported Pvalues were 2-sided and were considered as significant if less than .05. RESULTS A total of 141 recent HIV-1 seroconverters were identified. The median estimated time from initial exposure to the first detection of HIV-1 infection was 7.6 months. Overall, 67.4% had been infected through homosexual sex. The prevalence of genotypes associated with drug resistance in this population was 14.2% (20 of 141 genotypes). The distribution of resistance genotypes is summarized in table 1. Primary mutations at the RT gene were T215Y (4 subjects), M41L (4), M184V (2), Y181C (2), K103N (2), L210W (2), D67N (1), T69N (1), and K219Q (1). Moreover, 7 subjects presented with revertant forms at position 215 (C/D/L/N/S). At the protease gene, primary resistance mutations were L90M (3 subjects), M46L (2), and V82A (2). Five subjects had resistance mutations to 11 drug family. Two of these subjects presented with mutations associated with resistance to nucleoside RT inhibitors and nonnucleoside RT inhibitors, and another 3 presented with mutations associated with resistance to nucleoside RT inhibitors and protease inhibitors. The overall proportions of primary drug-resistance mutations, by year of infection, were 33.3% for 1997, 29.4% for 1998, 20% for 1999, 14.3% for 2000, 3.4% for 2001, 15.4% for 2002, and 10.4% for 2003. When we used different periods of time, the proportions were 29% for 1997–1999, 5.6% for 2000– Downloaded from https://academic.oup.com/cid/article/41/2/227/530871 by UNIVERSIDAD DE VALLADOLID. BIBLIOTECA user on 09 March 2021 HIV/AIDS •CID 2005:41 (15 July) •229 Table 1. Characteristics of patients with recent HIV-1 seroconversion who harbor drug-resistant virus. Patient Year of seroconversion Estimated duration of HIV infection, months Risk group Plasma HIV RNA level, copies/mL CD4 cell count, cells/mL Drug-resistance mutations RT Protease 1 1997 12 MSM 2880 472 T215L, K219Q … 2 1997 11 MSM 1925 717 T215Y … 3 1997 6 Heterosexual 500 Unknown M41L … 4 1998 12 Heterosexual 8876 545 M41L, L210W, T215D … 5 1998 12 MSM Unknown Unknown M41L, D67N, L210W, T215Y, Y181C … 6 1998 12 Heterosexual 13,070 678 M184V M46L, L90M 7 1998 7 MSM 39,420 689 T215Y … 8 1998 12 IDU 9330 1302 M41L … 9 1999 4 Heterosexual 20,401 840 T215N … 10 2000 9 MSM 500,000 530 … M46L 11 2001 11 MSM Unknown Unknown M41L, T215 … 12 2002 12 MSM 187,459 736 M41L, T215C … 13 2002 11 MSM Unknown Unknown M41L, T215S V82A, L90M 14 2002 6 MSM 2464 1023 Y181C … 15 2002 3 MSM 500,000 420 T69N … 16 2003 11 MSM 65,385 656 M41L, T215Y V82A, L90M 17 2003 3 Heterosexual 500,000 Unknown T215S … 18 2003 12 Heterosexual Unknown Unknown M184V, K103N … 19 2003 9 MSM 123,761 805 M41L … 20 2003 10 Heterosexual 75,000 257 K103N … NOTE. IDU, injection drug user; MSM, men who have sex with men; RT, reverse transcriptase. 2001, and 12.5% for 2002–2003. There was a significant decrease between the first and second periods ( ), andPp.014 there was a rebound between the second and third periods, although this did not achieve statistical significance ( )Pp.211 (figure 1). All but 2 patients were infected with HIV-1 subtype B viruses. One of the remaining 2 subjects presented with subtype C virus in 2001, and the other presented with a BG recombinant (CRF14_BG) virus in 2003. At total of 8388 patients with chronic HIV-1 infection seen during 1997–2003 were examined. Only 1 plasma virus load determination from each patient per year was evaluated. With use of a detection limit of 500 HIV-1 RNA copies/mL, undetectable virus loads were found for 44.6% of patients in 1997 and 48.6% in 1998; with use of a lower detection limit of 50 copies/mL, undetectable virus loads were noted for 37.5% of patients in 1999, 47.5% in 2000, 52.9% in 2001, 39.7% in 2002, and 58.1% in 2003. To make the threshold for viremia uniform, we estimated the virus loads for samples collected in 1997 and 1998 that harbored !50 copies/mL instead of !500 copies/mL. In prior studies [18–20], ∼75% of individuals with virus loads of !500 copies/mL in fact had virus loads of !50 copies/mL. With this assumption, the proportions of patients with virus loads of !50 copies/mL in 1997 and 1998 were indirectly estimated to be 33.4% and 34.6%, respectively. A significant inverse correlation between yearly rates of transmission of drug-resistant viruses and the proportion of patients with chronic HIV-1 carriage and undetectable virus loads was found ( , by Spearman’s test; ). Figure 2 rp⫺0.955 Pp.001 shows the relationship between the proportion of individuals with new HIV-1 infection who had drug-resistance mutations and the effect of antiretroviral therapy on plasma virus load in chronic carriers throughout the study period. DISCUSSION The widespread use of HAART has lead to a dramatic reduction in the morbidity and mortality of HIV-1–infected individuals [14]. A reduction in HIV-1 load—often to undetectablelevels— is usually seen in patients who are receiving HAART. Given that virus load titers correlate with the transmission risk for HIV-1, either from mother to child [21, 22] or to sex partners [16], it should not be surprising to find lower infectiousness for patients who are receiving HAART [23]. However, virological failure may appear after exposure to suboptimal therapy or as consequence of poor compliance with treatment, allowing drug-resistant viruses to emerge [1]. If individuals who harbor drug-resistant viruses continue to engage in high-risk practices, transmission of drug-resistant strains may occur, as was noticed soon after antiretroviral therapy was first introduced [24]. Downloaded from https://academic.oup.com/cid/article/41/2/227/530871 by UNIVERSIDAD DE VALLADOLID. BIBLIOTECA user on 09 March 2021 230 •CID 2005:41 (15 July) •HIV/AIDS Figure 1. Rate of drug-resistance mutations in patients who had recent HIV-1 seroconversion and the proportion of patients with chronic HIV carriage who had undetectable virus loads, 1997–2003. For 1997 and 1998, the percentage of subjects with an HIV RNA level of !50 copies/mL was estimated. In our study, 114% of recent HIV-1 seroconverters harbored drug-resistant viruses. Fluctuations over time were noticed, with the highest rate of transmission of drug-resistant strains occurring between 1997 and 1999, followed by a reduction in 2000–2001 and a rebound in 2002–2003. These results are in agreement with trends reported in other western European countries [25–27]. Recent decreases in the rate of transmission of drug-resistant HIV-1 have correlated with increases in the transmission of non-B subtypes in France, Switzerland, and Italy [28–30]. However, this was not observed in our study (we found only 2 subjects who had recently been infected with non- B strains) and has not been documented in other studies from Spain [31] in which subtype B continues to be, by far, the most predominant transmitted HIV-1 variant. Differences in the proportion of patients with chronic HIV- 1 infection for whom HAART failed could explain our findings for recent HIV-1 seroconverters. We analyzed the proportion of patients with chronic HIV-1 carriage who had undetectable virus loads, which mostly reflects the success of HAART in the overall population. By contrary, those with detectable virus loads are the potential transmitters. This group includes either patients who are antiretroviral naive or those for whom therapy is not successful. The latter is a larger population and is more likely to carry drug-resistant strains. The proportion of HIV-1–infected individuals with undetectable virus loads steadily increased from 1997 to 2001, reflecting more-widespread use of HAART and application of relatively more-aggressive treatment recommendations [32, 33]. The rate of drug resistance among recent HIV-1 seroconverters steadily decreased during that period, suggesting that a growing proportion of new HIV-1 infections involved treatment-naive subjects. In 2002, concerns of drug toxicity led to widespread use of drug holidays, structured treatment interruptions, and more-conservative treatment rules [14, 15, 34]. Together, this has resulted in an increased proportion of patients with chronic HIV-1 infection who have detectable virus loads. Individuals with prior antiretroviral exposure could then become potential transmitters of drug-resistant viruses [35, 36]. In accordance with this hypothesis, we found a rebound in the proportion of drug-resistant strains among recent HIV-1 seroconverters in the year 2002. In 2003, worries about the use of structured treatment interruptions and/or drug holidays [37], as well as the availability and extensive use of new potent drugs (lopinavir/ritonavir and tenofovir) [38, 39], seemed to revert the situation. Currently more patients with undetectable viremia are seen again among chronic HIV-1 carriers, and lower drug resistance rates are found among HIV-1 seroconverters. Our study has several limitations. First, the number of HIV- 1 seroconverters varied significantly from year to year. This is mainly because of the introduction of new assays for the diagnosis of HIV-1 infection in recent years [40] that have allowed the simultaneous detection of HIV-1 antigen and antibodies, and because of a more active search for HIV-1 seroconverters; in conjunction, these factors resulted in a higher rate of identification of primary HIV-1 infections during recent years. Sec- Downloaded from https://academic.oup.com/cid/article/41/2/227/530871 by UNIVERSIDAD DE VALLADOLID. BIBLIOTECA user on 09 March 2021 HIV/AIDS •CID 2005:41 (15 July) •231 ond, the proportion of patients with undetectable virus loads was used as a surrogate marker for the effectiveness of HAART. However, some long-term nonprogressors may also have undetectable virus loads without having received any antiretroviral therapy [41]. In our population of chronic carriers, we identified only 20 individuals who might be considered to belong to this category; therefore, their impact was negligible. Third, the population of potential transmitters we examined was quite heterogeneous. On one hand, it included patients with no prior exposure to therapy, but it also included subjects for whom antiretroviral therapy failed. Only the latter group might harbor drug-resistant strains more frequently. On the other hand, different levels of detectable virus may account for differences of transmission efficiency [42, 43], and this aspect was not assessed in our study. With all of these limitations in mind, however, we feel that our data support the hypothesis that the appropriate use of HAART is associated with a lower rate of transmission of drug-resistant viruses. In this context, although new HIV-1 infections may continue to occur, they are likely to derive from subjects who are antiretroviral naive, who rarely transmit drugresistant strains. In summary, higher proportions of virological suppression in chronic HIV-1 carriers associated with the use of HAART correlate with lower rates of transmission of drug-resistant viruses among individuals with new HIV-1 infection in a given community. Antiretroviral therapy has benefits for people other than those who are receiving treatment, as recently highlighted by others [44], and this should be emphasized, particularly in the light of recent increased sexual risk behaviors among highrisk groups [45–47] that result from a misperception that HIV- 1 infection is no longer a deadly illness. Acknowledgments We would like to thank Angelica Corral for his excellent technical assistance and Prof. Juan Gonzalez-Lahoz for his continuous support. Financial support. Fundacio´n Investigacio´n y Educacio´n en SIDA, Redes de Investigacio´n en SIDA (project 173), and Comunidad Auto´noma de Madrid. Potential conflicts of interest. V.S. has received grant/research support and speakers’ honorarium from and/or is on the clinical advisory boards for Bristol-Myers Squibb, Roche, Gilead, Abbott, GlaxoSmithKline, and Bayer. All other authors: no conflicts. References 1. Hirsch M, Brun-Ve´zinet F, Clotet B, et al. Antiretroviral drug resistance testing in adults infected with HIV-1: 2003 recommendations of an International AIDS Society–USA Panel. Clin Infect Dis 2003; 37: 113–28. 2. Brenner B, Routy J, Petrella M, et al. Persistence and fitness of multidrug-resistant HIV-1 acquired in primary infection. J Virol 2002; 76: 1753–61. 3. Garcia-Lerma G, MacInnes H, Bennet D, Weinstock H, Heneine W. Transmitted HIV-1 carrying D67N or K219Q evolve rapidly to zidovudine resistance in vitro and show a high replicative fitness in the presence of zidovudine [abstract]. Antivir Ther 2003; 8:S89. 4. Little S, Holte S, Routy J, et al. Antiretroviral drug resistance among patients recently infected with HIV. N Engl J Med 2002; 347:385–94. 5. Wensing A, Boucher C. Worldwide transmission of drug-resistant HIV. AIDS Rev 2003; 5:140–55. 6. Grant R, Hecht F, Warmerdam M, et al. Time trends in primary HIV- 1 drug resistance among recently infected persons. JAMA 2002; 288: 181–8. 7. Soriano V, Ledesma E. Second Spanish consensus on the use of drug resistance testing in clinical practice (Madrid, March 2000). The Spanish HIV Drug Resistance Panel. AIDS Rev 2000; 2:111–8. 8. The Euroguidelines Group for HIV Resistance. Clinical and laboratory guidelines for the use of HIV-1 drug resistance testing as a part of treatment management. AIDS 2001; 15:309–20. 9. Go´mez-Cano M, Rubio A, Puig T, et al. Prevalence of genotypic resistance to nucleoside analogues in antiretroviral-naive and antiretroviral-experienced HIV-infected patients in Spain. AIDS 1998; 12: 1015–20. 10. Puig T, Pe´rez-Olmeda M, Rubio A, et al. Prevalence of genotypic resistance to nucleoside analogues and protease inhibitors in Spain. AIDS 2000; 14:727–32. 11. Gallego O, Ruiz L, Vallejo A, et al. Changes in the rate of genotypic resistance to antiretroviral drugs in Spain. AIDS 2001; 15:1894–6. 12. Briones C, Pe´rez-Olmeda M, Rodriguez C, del Romero J, Hertogs K, Soriano V. Primary genotypic and phenotypic HIV-1 drug resistance in recent seroconvertors in Madrid. J Acquir Immune Defic Syndr 2001; 26:145–50. 13. Pe´rez-Olmeda M, Del Romero J, Rubio A, et al. Primary HIV-1 drug resistance in Spain before and after the introduction of protease inhibitors. J Med Virol 2001; 63:85–7. 14. Yeni P, Hammer S, Hirsch M, et al. Treatment for adult HIV infection: 2004 recommendations of the International AIDS Society–USA Panel. JAMA 2004; 292:251–65. 15. Department of Health and Human Services Panel. Guidelines for the use of antiretroviral agents in HIV-1 infected adults and adolescents. November 2004. Available at: http://www.aidsinfo.gov. Accessed 15 December 2004. 16. Quinn T, Wawer M, Sewankambo N, et al. Viral load and heterosexual transmission of HIV-1. Rakai Project Study Group. N Engl J Med 2000; 342:921–9. 17. Hue S, Clewley J, Cane P, Pillay D. HIV-1 pol gene variation is sufficient for reconstruction of transmissions in the era of antiretroviral therapy. AIDS 2004; 18:719–28. 18. Eron J, Murphy R, Peterson D, et al. A comparison of stavudine, didanosine and indinavir with zidovudine, lamivudine and indinavir for the initial treatment of HIV-1 infected individuals: selection of thymidine analog regimen therapy (START II). AIDS 2000; 14:1601–10. 19. Arnaiz J, Mallolas J, Podzamczer D, et al. Continued indinavir versus switching to indinavir/ritonavir in HIV-infected patients with suppressed viral load. AIDS 2003; 17:831–40. 20. Staszewski S, Keiser P, Montaner J, et al. Abacavir-lamivudine-zido- vudine vs indinavir-lamivudine-zidovudine in antiretroviral-naı¨ve HIV-infected adults: a randomized equivalence trial. JAMA 2001; 285: 1155–63. 21. Ayouba A, Tene G, Cunin P, et al. Low rate of mother to child transmission of HIV-1 after nevirapine intervention in a pilot study public health program in Yaounde, Cameroon. J Acquir Immune Defic Syndr 2003; 34:274–80. 22. Jamieson D, Sibailly T, Sadek R, et al. HIV-1 viral load and other risk factors for mother to child transmission of HIV-1 in breast-feeding population in Cote d’Ivoire. J Acquir Immune Defic Syndr 2003; 34: 430–6. 23. Porco T, Martin J, Page-Shafer K, et al. Decline in HIV infectivity following the introduction of highly active antiretroviral therapy. AIDS 2004; 18:81–8. 24. Erice A, Mayers D, Strike D, et al. Primary infection with zidovudineresistant HIV-1. N Engl J Med 1993; 328:1163–5. 25. Wensing A, van de Vijver D, Asjo B, et al. Prevalence of transmitted Downloaded from https://academic.oup.com/cid/article/41/2/227/530871 by UNIVERSIDAD DE VALLADOLID. BIBLIOTECA user on 09 March 2021 232 •CID 2005:41 (15 July) •HIV/AIDS drug resistance in Europe is largely influenced by the presence of non- B sequences: analysis of 1400 patients from 16 countries: the CATCH study. Antivir Ther 2003; 8:S131. 26. Duwe S, Brunn M, Altmann D, et al. Frequency of genotypic and phenotypic drug-resistant HIV-1 among therapy naı¨ve patients of the German seroconverter study. J Acquir Immune Defic Syndr 2001; 26: 266–73. 27. UK collaborative group of monitoring the transmission of HIV drug resistance. Analysis of prevalence of HIV-1 drug resistance in primary infections in the United Kingdom. BMJ 2001; 322:1087–8. 28. Harzic M, Pellegrin I, Deveau C, et al. Genotypic drug resistanceduring HIV-1 primary infection in France (1996–1999): frequency and response to treatment. AIDS 2002; 16:793–6. 29. Yerly S, Vora S, Rizzardi P, et al. Acute HIV infection: impact on the spread of HIV and transmission of drug resistance. AIDS 2001; 15: 2287–92. 30. Balotta C, Facchi G, Violin M, et al. Increasing prevalence of nonclade B HIV-1 strains in heterosexual men and women, as monitored by analysis of reverse transcriptase and protease sequences. J Acquir Immune Defic Syndr 2001; 27:499–505. 31. De Mendoza C, del Romero J, Rodriguez C, Corral A, Soriano V. Decline in the rate of genotypic resistance to antiretroviral drugs in recent HIV seroconverters in Madrid. AIDS 2002; 16:1830–2. 32. Carpenter C, Fischl M, Hammer S, et al. Antiretroviral therapy for HIV infection in 1998: updated recommendations of the International AIDS Society–USA Panel. JAMA 1998; 280:78–86. 33. Carpenter C, Cooper D, Fischl M, et al. Antiretroviral therapy in adults: updated recommendation of the International AIDS Society–USA Panel. JAMA 2000; 283:381–90. 34. Lori F, Foli A, Maserati R, et al. Control of HIV during a structured treatment interruption in chronically infected individuals with vigorous T cell response. HIV Clin Trials 2002; 3:115–24. 35. Metzner K, Bonhoeffer S, Fischer M, et al. Emergence of minor populations of HIV-1 carrying the M184V and L90M mutations in subjects undergoing structured treatment interruptions. J Infect Dis 2003; 188: 1433–43. 36. Teicher E, Casagrande T, Vittecoq D. Enhanced risk of HIV sexual transmission during structured treatment interruptions. Sex Transm Infect 2003; 79:74. 37. Hirschel B. Beware of drug holidays before HIV salvage therapy. N Engl J Med 2003; 349:827–8. 38. De Mendoza C, Martin-Carbonero L, Barreiro P, et al. Salvage treatment with lopinavir/ritonavir (Kaletra) in HIV-infected patients failing all current antiretroviral drug families. HIV Clin Trials 2002; 3:304–9. 39. Schooley R, Ruane P, Myers R. Tenofovir DF in antiretroviral experienced patients: results from a 48-week, randomized, double-blind study. AIDS 2002; 16:1257–64. 40. Pilcher C, Eron J, Galvin S, Gay S, Cohen M. Acute HIV revisited: new opportunities for treatment and prevention. J Clin Invest 2004; 113:937–45. 41. Berta B, Toro C, Paxinos E, et al. Differences in disease progression in a cohort of long-term non-progressors after more than 16 years of HIV-1 infection. AIDS 2004; 18:1109–16. 42. Leynaert B, Downs A, de Vincenzi I. Heterosexual transmission of HIV: variability of infectivity throughout the course of infection. European Study Group on Heterosexual Transmission of HIV. Am J Epidemiol 1998; 148:88–96. 43. Wawer M, Serwadda D, Li X, et al. HIV-1 transmission per coital act, by stage of HIV infection in the HIV + index partner, in discordant couples, Rakai, Uganda [abstract 40]. In: Program and abstracts of the 10th Conference on Retroviruses and Opportunistic Infections (Boston). Alexandria, VA: Foundation for Retrovirology and Human Health, 2003:71. 44. Holmberg S, Palella F, Lichtenstein K, Havlir D. The case for earlier treatment of HIV infection. Clin Infect Dis 2004; 39:1699–704. 45. Elford J, Bolding G, Sherr L. High-risk sexual behaviour increases among London gay men between 1998 and 2001: what is the role of HIV optimism? AIDS 2002; 16:1537–44. 46. Erbelding E, Chung S, Kamb M, Irwin K, Rompalo A. New sexually transmitted diseases in HIV-infected patients: markers for ongoing HIV transmission behaviour. J Acquir Immune Defic Syndr 2003; 33:247–52. 47. McGowan, Shah S, Ganea C, et al. Risk behaviour for transmission of HIV among HIV-seropositive individuals in an urban setting. Clin Infect Dis 2004; 38:122–7. Downloaded from https://academic.oup.com/cid/article/41/2/227/530871 by UNIVERSIDAD DE VALLADOLID. BIBLIOTECA user on 09 March 2021