Risk Factors for Severe Outcomes following 2009 Influenza A (H1N1) Infection: A Global Pooled Analysis
Background:
Since the start of the 2009 influenza A pandemic (H1N1pdm), the World Health Organization and its member states have gathered information to characterize the clinical severity of H1N1pdm infection and to assist policy makers to determine risk groups for targeted control measures.
Methods and Findings:
Data were collected on approximately 70,000 laboratory-confirmed hospitalized H1N1pdm patients, 9,700 patients admitted to intensive care units (ICUs), and 2,500 deaths reported between 1 April 2009 and 1 January 2010 from 19 countries or administrative regions—Argentina, Australia, Canada, Chile, China, France, Germany, Hong Kong SAR, Japan, Madagascar, Mexico, the Netherlands, New Zealand, Singapore, South Africa, Spain, Thailand, the United States, and the United Kingdom—to characterize and compare the distribution of risk factors among H1N1pdm patients at three levels of severity: hospitalizations, ICU admissions, and deaths. The median age of patients increased with severity of disease. The highest per capita risk of hospitalization was among patients <5 y and 5–14 y (relative risk [RR] = 3.3 and 3.2, respectively, compared to the general population), whereas the highest risk of death per capita was in the age groups 50–64 y and ≥65 y (RR = 1.5 and 1.6, respectively, compared to the general population). Similarly, the ratio of H1N1pdm deaths to hospitalizations increased with age and was the highest in the ≥65-y-old age group, indicating that while infection rates have been observed to be very low in the oldest age group, risk of death in those over the age of 64 y who became infected was higher than in younger groups. The proportion of H1N1pdm patients with one or more reported chronic conditions increased with severity (median = 31.1%, 52.3%, and 61.8% of hospitalized, ICU-admitted, and fatal H1N1pdm cases, respectively). With the exception of the risk factors asthma, pregnancy, and obesity, the proportion of patients with each risk factor increased with severity level. For all levels of severity, pregnant women in their third trimester consistently accounted for the majority of the total of pregnant women. Our findings suggest that morbid obesity might be a risk factor for ICU admission and fatal outcome (RR = 36.3).
Conclusions:
Our results demonstrate that risk factors for severe H1N1pdm infection are similar to those for seasonal influenza, with some notable differences, such as younger age groups and obesity, and reinforce the need to identify and protect groups at highest risk of severe outcomes.
: Please see later in the article for the Editors' Summary
Vyšlo v časopise:
Risk Factors for Severe Outcomes following 2009 Influenza A (H1N1) Infection: A Global Pooled Analysis. PLoS Med 8(7): e32767. doi:10.1371/journal.pmed.1001053
Kategorie:
Research Article
prolekare.web.journal.doi_sk:
https://doi.org/10.1371/journal.pmed.1001053
Souhrn
Background:
Since the start of the 2009 influenza A pandemic (H1N1pdm), the World Health Organization and its member states have gathered information to characterize the clinical severity of H1N1pdm infection and to assist policy makers to determine risk groups for targeted control measures.
Methods and Findings:
Data were collected on approximately 70,000 laboratory-confirmed hospitalized H1N1pdm patients, 9,700 patients admitted to intensive care units (ICUs), and 2,500 deaths reported between 1 April 2009 and 1 January 2010 from 19 countries or administrative regions—Argentina, Australia, Canada, Chile, China, France, Germany, Hong Kong SAR, Japan, Madagascar, Mexico, the Netherlands, New Zealand, Singapore, South Africa, Spain, Thailand, the United States, and the United Kingdom—to characterize and compare the distribution of risk factors among H1N1pdm patients at three levels of severity: hospitalizations, ICU admissions, and deaths. The median age of patients increased with severity of disease. The highest per capita risk of hospitalization was among patients <5 y and 5–14 y (relative risk [RR] = 3.3 and 3.2, respectively, compared to the general population), whereas the highest risk of death per capita was in the age groups 50–64 y and ≥65 y (RR = 1.5 and 1.6, respectively, compared to the general population). Similarly, the ratio of H1N1pdm deaths to hospitalizations increased with age and was the highest in the ≥65-y-old age group, indicating that while infection rates have been observed to be very low in the oldest age group, risk of death in those over the age of 64 y who became infected was higher than in younger groups. The proportion of H1N1pdm patients with one or more reported chronic conditions increased with severity (median = 31.1%, 52.3%, and 61.8% of hospitalized, ICU-admitted, and fatal H1N1pdm cases, respectively). With the exception of the risk factors asthma, pregnancy, and obesity, the proportion of patients with each risk factor increased with severity level. For all levels of severity, pregnant women in their third trimester consistently accounted for the majority of the total of pregnant women. Our findings suggest that morbid obesity might be a risk factor for ICU admission and fatal outcome (RR = 36.3).
Conclusions:
Our results demonstrate that risk factors for severe H1N1pdm infection are similar to those for seasonal influenza, with some notable differences, such as younger age groups and obesity, and reinforce the need to identify and protect groups at highest risk of severe outcomes.
: Please see later in the article for the Editors' Summary
Zdroje
1. Centers for Disease Control and Prevention 2009 Update: swine influenza A (H1N1) infections—California and Texas, April 2009 MMWR Morb Mortal Wkly Rep 58 435 437 Available: http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5816a7.htm. Accessed 22 January 2010
2. World Health Organization 2009 Swine influenza—update 3. Available: http://www.who.int/csr/don/2009_04_27/en/index.html. Accessed 22 January 2010
3. ChanM 2009 April 25 Swine influenza: statement by WHO Director-General, Dr Margaret Chan. Available: http://www.who.int/mediacentre/news/statements/2009/h1n1_20090425/en/index.html. Accessed 21 January 21 2010
4. World Health Organization 2010 Evolution of a pandemic: A(H1N1) 2009, April 2009–March 2010 Geneva World Health Organization
5. National Center for Immunization and Respiratory Diseases 2009 Use of influenza A (H1N1) 2009 monovalent vaccine. Recommendations of the Advisory Committee on Immunization Practices (ACIP), 2009. MMWR Recomm Rep 58 RR-10 1 8
6. FioreAShayDBroderKUyekiTMootreyG 2009 Prevention and control of influenza, recommendations of the Advisory Committee on Immunization Practices (ACIP), 2008. MMWR Recomm Rep 57 RR-7 1 60
7. MereckieneJCotterSNicollALevy-BruhlDFerroA 2008 National seasonal influenza vaccination survey in Europe, 2008. Euro Surveill 13 pii: 19017
8. DoddLMcNeilSAFellDBAllenVMCoombsA 2007 Impact of influenza exposure on rates of hospital admissions and physician visits because of respiratory illness among pregnant women. CMAJ 176 463 468
9. FreemanDWBarnoA 1959 Deaths from Asian influenza associated with pregnancy. Am J Obstet Gynecol 78 1172 1175
10. HarrisJW 1919 Influenza occurring in pregnant women. JAMA 72 978 980
11. NeuzilKMReedGWMitcheEFSimonsenLGriffinMR 1998 Impact of influenza on acute cardiopulmonary hospitalizations in pregnant women. Am J Epidemiol 148 1094 1102
12. World Health Organization 2009 Clinical features of severe cases of pandemic influenza. Pandemic (H1N1) 2009 briefing note 13. Available: http://www.who.int/csr/disease/swineflu/notes/h1n1_clinical_features_20091016/en/index.html. Accessed 19 May 2011
13. The ANZIC Influenza Investigators 2009 Critical care services and 2009 H1N1 influenza in Australia and New Zealand. N Engl J Med 361 1925 1934 Available: http://www.nejm.org/doi/full/10.1056/NEJMoa0908481#t=article. Accessed 19 May 2011
14. Centers for Disease Control and Prevention 2009 Deaths related to 2009 pandemic influenza A (H1N1) among American Indian/Alaska Natives—12 states, 2009. MMWR Morb Mortal Weekly Rep 58 1341 1344
15. DonaldsonLJRutterPDEllisBMGreavesFECMyttonOT 2009 Mortality from pandemic A/H1N1 2009 influenza in England: public health surveillance study. BMJ 339 b5213
16. BinSaeedA 2010 Characteristics of pandemic influenza A (H1N1) infection in patients presenting to a university hospital in Riyadh, Saudi Arabia. Ann Saudi Med 30 59 62
17. Centers for Disease Control and Prevention 2009 Novel influenza A (H1N1) virus infections in three pregnant women—United States, April–May 2009. MMWR Morb Mortal Weekly Rep 58 497 500
18. Centers for Disease Control and Prevention 2009 Hospitalized patients with novel influenza A (H1N1) virus infection—California, April–May, 2009. MMWR Morb Mortal Weekly Rep 58 536 541
19. PalaciosGHornigMCisternaDSavjiNBussettiA 2009 Streptococcus pneumoniae coinfection is correlated with the severity of H1N1 pandemic influenza. PLoS ONE 4 e8540 doi:10.1371/journal.pone.0008540
20. FuhrmanCBonmarinIPatyADuportNChironE 2010 Severe hospitalised 2009 pandemic influenza A(H1N1) cases in France, 1 July–15 November 2009. Euro Surveill 15 pii: 19463 Available: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19463. Accessed 19 May 2011
21. LouieJKAcostaMWinterKJeanCGavaliS 2009 Factors associated with death or hospitalization due to pandemic 2009 influenza A(H1N1) infection in California. JAMA 302 1896 1902
22. ChienYSuCTsaiHHuangSChuangJ 2009 The first 100 hospitalized severe complicated influenza cases caused by 2009 pandemic influenza A (H1N1) in Taiwan. Taiwan Epidemiology Bulletin. Available: http://teb.cdc.gov.tw/public/Attachment/23552_25-10-%E8%8B%B12-692-707.pdf. Accessed 19 May 2011
23. ZarychanskiRStuartTLKumarADoucetteSElliottL 2010 Correlates of severe disease in patients with 2009 pandemic influenza (H1N1) virus infection. CMAJ 182 257 264
24. CullenGMartinJO'DonnellJBolandMCannyM 2009 Surveillance of the first 205 confirmed hospitalised cases of pandemic H1N1 influenza in Ireland, 28 April–3 October 2009. Euro Surveill 14 pii: 19389
25. DenholmJGordonCJohnsonPHewagamaSStuartR 2010 Hospitalised adult patients with pandemic (H1N1) 2009 influenza in Melbourne, Australia. MJA 192 84 86
26. YangPDengYPangXShiWLiX 2010 Severe, critical and fatal cases of 2009 H1N1 influenza in China. J Infect 61 277 283 doi:10.1016/j.jinf.2010.07.010
27. ShimadaTGuYKamiyaHKomiyaNOdairaF 2010 Epidemiology of influenza A(H1N1)v virus infection in Japan, May–June 2009. Euro Surveill 14 pii: 19244 Available: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19244. Accessed 19 May 2011
28. PoggenseeGGilsdorfABudaSEckmannsTClausH 2010 The first wave of pandemic influenza (H1N1) 2009 in Germany: from initiation to acceleration. BMC Infect Dis 10 155 doi:110.1186/1471-2334-1110-1155
29. van 't KloosterTWieldersCDonkerTIskenLMeijerA 2010 Surveillance of hospitalisations for 2009 pandemic influenza A(H1N1) in the Netherlands, 5 June–31 December 2009. Euro Surveill 15 pii: 19461
30. HahnéSDonkerTMeijerATimenAvan SteenbergenJ 2009 Epidemiology and control of influenza A(H1N1)v in the Netherlands: the first 115 cases. Euro Surveill 14 pii: 19267 Available: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19267. Accessed 19 May 2011
31. VriendHJHahnéSJMDonkerTMeijerATimenA 2009 De nieuwe influenza A(H1N1)-epidemie in Nederland. Epidemiologische gegevens over de periode 30 april–14 augustus 2009. Ned Tijdschr Geneeskd 153 A969
32. van der SandeMABvan der HoekWHooiveldMDonkerGAvan SteenbergenJE 2009 Bestrijding van de nieuwe influenza A (H1N1). II. Epidemiologie en niet-medicamenteuze maatregelen. Ned Tijdschr Geneeskd 153 A771
33. DijkstraFvan 't KloosterTMBrandsemaPvan Gageldonk-LafeberABMeijerA 2010 Jaarrapportage surveillance respiratoire infectieziekten 2009. Bilthoven: Rijksinstituut voor Volksgezondheid en Milieu, 2010. RIVM RIVM-briefrapportnummer: 210231006. Available: http://www.rivm.nl/bibliotheek/rapporten/210231006.pdf. Accessed 19 May 2011
34. Institut de Veille Sanitaire 2009 December 16 Surveillance de la grippe A (H1N1) 2009 en France: outils et méthodes. Available: http://www.invs.sante.fr/surveillance/grippe_dossier/docs_professionnels/methodo_surveillance_grippe_161209.pdf. Accessed 19 May 2011
35. SkarbinskiJJainSBramleyALeeEJHuangJ 2011 Hospitalized patients with 2009 pandemic influenza A (H1N1) virus infection in the United States—September–October 2009. Clin Infect Dis 52 Suppl 1 S50 S59
36. JainSKamimotoLBramleyAMSchmitzAMBenoitSR 2009 Hospitalized patients with 2009 H1N1 influenza in the United States, April–June 2009. N Engl J Med 361 1935 1944
37. UK Health Protection Agency 2010 Sources of UK flu data: influenza surveillance in the United Kingdom. Available: http://www.hpa.org.uk/webw/HPAweb&HPAwebStandard/HPAweb_C/1195733821514?p=1191942171484. Accessed 19 May 2011
38. RandrianasoloLRaoelinaYRatsitorahinaMRavolomananaLAndriamandimbyS 2010 Sentinel surveillance system for early outbreak detection in Madagascar. BMC Public Health 10 31
39. CutterJAngLWLaiFYSubramonyHMaS 2010 Outbreak of pandemic influenza A (H1N1-2009) in Singapore, May to September 2009. Ann Acad Med Singapore 39 273 282
40. Sierra MorosMJVázquez TorresMSanta-Olalla PeraltaPLimia SánchezACortes GarcíaM 2010 Epidemiological surveillance activities during the 2009 influenza pandemic in Spain. Lessons learnt one year after. Rev Esp Salud Publica 84 463 480
41. Santa-Olalla PeraltaPCortes-GarciaMVicente-HerreroMCastrillo-VillamandosCArias-BohigasP 2010 Risk factors for disease severity among hospitalised patients with 2009 pandemic influenza A (H1N1) in Spain, April–December 2009. Euro Surveill 15 pii: 19667
42. Santa-Olalla PeraltaPCortes GarcíaMLimia SánchezAAndrés PradoJPachón del AmoI 2010 Critically ill patients with 2009 pandemic influenza A (H1N1) infection in Spain: factors associated with death, April 2009–January 2010. Rev Esp Salud Publica 84 547 568
43. BakerMGWilsonNHuangQSPaineSLopezL 2009 Pandemic influenza A(H1N1)v in New Zealand: the experience from April to August 2009. Euro Surveill 14 pii: 19319
44. HuangQSBandaranayakeDLopezLDPirieRPeaceyM 2009 Surveillance for the 2009 pandemic influenza A (H1N1) virus and seasonal influenza viruses - New Zealand, 2009. MMWR Morb Mortal Wkly Rep 58 918 921
45. YuHLiaoQYuanYZhouLXiangN 2010 Effectiveness of oseltamivir on disease progression and viral RNA shedding in patients with mild pandemic 2009 influenza A H1N1: opportunistic retrospective study of medical charts in China. BMJ 341 c4779
46. YuHFengZUjekiTMLiaoQZhouL 2011 Risk factors for severe illness with 2009 pandemic influenza A(H1N1) virus infection in China. Clin Infect Dis 52 457 465
47. CampbellARodinRKroppRMaoYHongZ 2010 Risk of severe outcomes among patients admitted to hospital with pandemic (H1N1) influenza. CMAJ 182 349 355
48. HelfertyMVachonJTarasukJRodinRSpikaJ 2011 Canadian pandemic H1N1 cases: a description of the changing epidemiology of hospitalizations and deaths in the first and second waves. CMAJ In press
49. KongWM 2000 A review on the Hong Kong influenza surveillance system. Public Health Epidemiology Bull 9
50. United Nations Population Division 2009 World population prospects: the 2008 revision population database. http://esa.un.org/unpd/wpp/unpp/panel_population.htm
51. HigginsJThompsonSG 2002 Quantifying heterogeneity in a meta-analysis. Stat Med 21 1539 1558
52. SimmondsMCHigginsJP 2007 Covariate heterogeneity in meta-analysis: criteria for deciding between meta-regression and individual patient data. Stat Med 26 2982 2999
53. PebodyRGMcLeanEZhaoHClearyPBracebridgeS 2010 Pandemic influenza A (H1N1) 2009 and mortality in the United Kingdom: risk factors for death, April 2009 to March 2010. Euro Surveill 15 pii: 19571
54. VaillantLLa RucheGTarantolaABarbozaP epidemic intelligence team at InVS 2009 Epidemiology of fatal cases associated with pandemic H1N1 influenza 2009. Euro Surveill 14 pii: 19309
55. BettingerJASauvéLJScheifeleDWMooreDVaudryW 2010 Pandemic influenza in Canadian children: A summary of hospitalized pediatric cases. Vaccine 28 3180 3184
56. LemaitreMCarratF 2010 Comparative age distribution of influenza morbidity and mortality during seasonal influenza epidemics and the 2009 H1N1 pandemic. BMC Infect Dis 10 162
57. KamigakiTOshitaniH 2009 Epidemiological characteristics and low case fatality rate of pandemic (H1N1) 2009 in Japan. PLoS Curr 1 RRN1139
58. HanslikTBoellePFlahaultA 2010 Preliminary estimation of risk factors for admission to intensive care units and for death in patients infected with A(H1N1)2009 influenza virus, France, 2009–2010. PLoS Curr 2 RRN1150
59. WuJTMaESLeeCKChuDKHoPL 2010 The infection attack rate and severity of 2009 pandemic H1N1 influenza in Hong Kong. Clin Infect Dis 51 1184 1191
60. MillerEHoschlerKHardelidPStanfordEAndrewsN 2010 Incidence of 2009 pandemic influenza A H1N1 infection in England: a cross-sectional serological study. Lancet 375 1100 1108
61. PresanisAMDe AngelisDHagyAReedC The New York City Swine Flu Investigation Team 2009 The severity of pandemic H1N1 influenza in the United States, from April to July 2009: a Bayesian analysis. PLoS Med 6 e1000207 doi:10.1371/journal.pmed.1000207
62. WatsonLTurkFJamesPHolgateST 2007 Factors associated with mortality after an asthma admission: A national United Kingdom database analysis. Respir Med 101 1659 1664
63. JamiesonDJHoneinMARasmussenSAWilliamsJLSwerdlowDL 2009 H1N1 2009 influenza virus infection during pregnancy in the USA. Lancet 374 451 458
64. KumarAZarychanskiRPintoRCookDJMarshallJ 2009 Critically ill patients with 2009 influenza A(H1N1) infection in Canada. JAMA 302 1872 1879
65. CreangaAAJohnsonTFGraitcerSBHartmanLKAl-SamarraiT 2010 severity of 2009 pandemic influenza A (H1N1) virus infection in pregnant women. Obstet Gynecol 115 717 726
66. The ANZIC Influenza Investigators and Australasian Maternity Outcomes Surveillance System 2010 Critical illness due to2009 A/H1N1 influenza in pregnant and postpartum women: population based cohort study. BMJ 340 c1279 doi:1210.1136/bmj.c1279
67. ArcherBCohenCNaidooDThomasJMakungaC 2009 Interim report on pandemic H1N1 influenza virus infections in South Africa, April to October 2009: epidemiology and factors associated with fatal cases. Euro Surveill 14 pii: 19369
68. SistonAMRasmussenSAHoneinMAFryAMSeibK 2010 Pandemic 2009 influenza A(H1N1) virus illness among pregnant women in the United States. JAMA 303 1517 1525
69. JamiesonDTheilerRRasmussenS 2006 Emerging infections and pregnancy. Emerg Infect Dis 12 1638 1643
70. GoodnightWSoperD 2005 Pneumonia in pregnancy. Crit Care Med 33 S390 S397
71. Centers for Disease Control and Prevention 2009 Intensive-care patients with severe novel influenza A (H1N1) virus infection—Michigan, June 2009. MMWR Morb Mortal Weekly Rep 58 749 752
72. Dominguez-CheritGLapinskySEMaciasAEPintoREspinosa-PerezL 2009 Critically ill patients with 2009 influenza A(H1N1) in Mexico. JAMA 302 1880 1887
73. RelloJRodríguezAIbañezPSociasLCebrianJ 2009 Intensive care adult patients with severe respiratory failure caused by Influenza A (H1N1)v in Spain. Crit Care 13 R148
74. RodríguezASocíasLGuerreroJFigueiraJGonzálezN 2010 Gripe A pandémica en una unidad de cuidados intensivos: experiencia en España y Latinoamérica (Grupo Español de Trabajo de Gripe A Grave/Sociedad Española de Medicina Intensiva, Crítica y Unidades Coronarias). Med Intensiva 34 87 94
75. Centers for Disease Control and Prevention 2009 Patients hospitalized with 2009 pandemic influenza A (H1N1)—New York City, May 2009. MMWR Morb Mortal Weekly Rep 58 1436 1440
76. PlessaEDiakakisPGardelisJThiriosAKoletsiP 2010 Clinical features, risk factors, and complications among pediatric patients with pandemic influenza A (H1N1). Clin Pediatr (Phila) 49 777 781
77. MorganOBramleyAFowlkesAFreedmanDTaylorTH 2010 Morbid obesity as a risk factor for hospitalization and death due to 2009 pandemic influenza A(H1N1) disease. PLoS ONE 5 e9694 doi:9610.1371/journal.pone.0009694
78. Arizona Department of Health Services 2010 Arizona—Supplemental influenza summary MMWR Week 9 (2/28/10–3/6/10) Phoenix (Arizona) Arizona Department of Health Services
79. Fundação Nacional de Saúde 2009 Saúde indígena—informe técnico sobre influenza A H1N1. Influenza A (H1N1) em populações indígenas do Brasil. Informe Técnico n°06/2009. Available: http://www.funasa.gov.br/internet/desai/arquivos/informeTecnicoInfluenzaA_6.pdf. Accessed 30 May 2011
80. La RucheGTarantolaABarbozaPVaillantLGueguenJ 2009 The 2009 pandemic H1N1 influenza and indigenous populations of the Americas and the Pacific. Euro Surveill 14 pii: 19366
81. Australian Government Department of Health and Aging 2010 Australian influenza surveillance report no. 8, 2010. Available: http://www.healthemergency.gov.au/internet/healthemergency/publishing.nsf/Content/EB136394E79CA5E2CA2576A50010783A/File/ozflu-no8-2010.pdf. Accessed 19 May 2011
82. WebbSAPettilaVSeppeltIBellomoRBaileyM 2009 Critical care services and 2009 H1N1 influenza in Australia and New Zealand. N Engl J Med 361 1925 1934
83. WilsonNBakerM 2008 Ninety years on: what we still need to learn from “Black November” 1918 about pandemic influenza. N Z Med J 121 136 138
84. GroomAVJimCLaroqueMMasonCMcLaughlinJ 2009 Pandemic influenza preparedness and vulnerable populations in tribal communities. Am J Public Health 99 Suppl 2 S271 S278
85. JohnsonNPMuellerJ 2002 Updating the accounts: global mortality of the 1918–1920 “Spanish” influenza pandemic. Bull Hist Med 76 105 115
86. SubramonyHLaiFYAngLWCutterJLimPL 2010 An epidemiological study of 1348 cases of pandemic H1N1 influenza admitted to Singapore hospitals from July to September 2009. Ann Acad Med Singapore 39 283 290
Štítky
Interné lekárstvoČlánok vyšiel v časopise
PLOS Medicine
2011 Číslo 7
- Statinová intolerance
- Očkování proti virové hemoragické horečce Ebola experimentální vakcínou rVSVDG-ZEBOV-GP
- Co dělat při intoleranci statinů?
- Pleiotropní účinky statinů na kardiovaskulární systém
- DESATORO PRE PRAX: Aktuálne odporúčanie ESPEN pre nutričný manažment u pacientov s COVID-19
Najčítanejšie v tomto čísle
- Individualized Cost-Effectiveness Analysis
- GeneXpert—A Game-Changer for Tuberculosis Control?
- Screening for HIV-Associated Tuberculosis and Rifampicin Resistance before Antiretroviral Therapy Using the Xpert MTB/RIF Assay: A Prospective Study
- Treatment Outcomes and Cost-Effectiveness of Shifting Management of Stable ART Patients to Nurses in South Africa: An Observational Cohort