Saturation is a core guiding principle to determine sample sizes in qualitative research, yet little methodological research exists on parameters that influence saturation. Our study compared two approaches to assessing saturation: code saturation and meaning saturation. We examined sample sizes needed to reach saturation in each approach, what saturation meant, and how to assess saturation. Examining 25 in-depth interviews, we found that code saturation was reached at nine interviews, whereby the range of thematic issues was identified. However, 16 to 24 interviews were needed to reach meaning saturation where we developed a richly textured understanding of issues. Thus, code saturation may indicate when researchers have "heard it all," but meaning saturation is needed to "understand it all." We used our results to develop parameters that influence saturation, which may be used to estimate sample sizes for qualitative research proposals or to document in publications the grounds on which saturation was achieved.

Infectious and inflammatory diseases have repeatedly shown strong genetic associations within the major histocompatibility complex (MHC); however, the basis for these associations remains elusive. To define host genetic effects on the outcome of a chronic viral infection, we performed genome-wide association analysis in a multiethnic cohort of HIV-1 controllers and progressors, and we analyzed the effects of individual amino acids within the classical human leukocyte antigen (HLA) proteins. We identified >300 genome-wide significant single-nucleotide polymorphisms (SNPs) within the MHC and none elsewhere. Specific amino acids in the HLA-B peptide binding groove, as well as an independent HLA-C effect, explain the SNP associations and reconcile both protective and risk HLA alleles. These results implicate the nature of the HLA–viral peptide interaction as the major factor modulating durable control of HIV infection.

Durable control of human immunodeficiency virus (HIV) replication and lack of disease progression in the absence of antiretroviral therapy were studied in a military cohort of 4586 subjects. We examined groups of elite controllers (ie, subjects with plasma HIV RNA levels of <50 copies/mL; prevalence, 0.55% [95% confidence interval {CI}, 0.35%-0.80%]), viremic controllers (ie, subjects with plasma HIV RNA levels of 50-2000 copies/mL; prevalence, 3.34% [95% CI, 2.83%-3.91%]), and subjects with a lack of disease progression (ie, long-term nonprogressors [LTNPs]) through 7 years of follow-up (LTNP7s; prevalence, 3.32% [95% CI, 2.70%-4.01%]) or 10 years of follow-up (LTNP10s; prevalence, 2.04% [95% CI, 1.52%-2.68%]). For elite and viremic controllers, spontaneous virologic control was established early and was typically observed when the initial viral load measurement was obtained within 1 year of estimated seroconversion. Elite controllers had favorable time to development of AIDS (P=.048), a CD4 cell count of 350 cells/microL (P= .009), and more-stable CD4 cell trends, compared with viremic controllers. LTNPs defined by 10-year versus 7-year criteria had a longer survival time (P=.001), even after adjustment for differing periods of invulnerability (P= .042). Definitions of controllers and LTNPs describe distinct populations whose differing clinical outcomes improve with the stringency of criteria, underscoring the need for comparability between study populations.