CINXE.COM

Just a moment...

<!DOCTYPE html><html lang="en-US"><head><title>Just a moment...</title><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><meta http-equiv="X-UA-Compatible" content="IE=Edge"><meta name="robots" content="noindex,nofollow"><meta name="viewport" content="width=device-width,initial-scale=1"><style>*{box-sizing:border-box;margin:0;padding:0}html{line-height:1.15;-webkit-text-size-adjust:100%;color:#313131;font-family:system-ui,-apple-system,BlinkMacSystemFont,Segoe UI,Roboto,Helvetica Neue,Arial,Noto Sans,sans-serif,Apple Color Emoji,Segoe UI Emoji,Segoe UI Symbol,Noto Color Emoji}body{display:flex;flex-direction:column;height:100vh;min-height:100vh}.main-content{margin:8rem auto;max-width:60rem;padding-left:1.5rem}@media (width <= 720px){.main-content{margin-top:4rem}}.h2{font-size:1.5rem;font-weight:500;line-height:2.25rem}@media (width <= 720px){.h2{font-size:1.25rem;line-height:1.5rem}}#challenge-error-text{background-image:url(data:image/svg+xml;base64,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);background-repeat:no-repeat;background-size:contain;padding-left:34px}@media (prefers-color-scheme:dark){body{background-color:#222;color:#d9d9d9}}</style><meta http-equiv="refresh" content="390"></head><body class="no-js"><div class="main-wrapper" role="main"><div class="main-content"><noscript><div class="h2"><span id="challenge-error-text">Enable JavaScript and cookies to continue</span></div></noscript></div></div><script>(function(){window._cf_chl_opt={cvId: '3',cZone: "mh.bmj.com",cType: 'managed',cRay: '913fbc95f9758333',cH: 'FuSmZqw2ucyahOHPz1axevWZZ3chpDbUvJ3XY50Joy4-1739899738-1.2.1.1-i2_BQmi6dcH2dW7QG1b5apvmZZp8ox2JJ0hd43c.tyyill_ni2ZAfaIj5z5eW4EY',cUPMDTk: "\/lookup\/doi\/10.1136\/medhum-2019-011766?__cf_chl_tk=GxbLfn7qqd5HCJUpKYm13HQb6yY7fDdyhPKSVzFndKM-1739899738-1.0.1.1-UWGVEgw22ufGK04yI.jmlzKyMSBIwFPxU3kgZQSuquY",cFPWv: 'g',cITimeS: '1739899738',cTTimeMs: '1000',cMTimeMs: '390000',cTplC: 0,cTplV: 5,cTplB: 'cf',cK: "unsupported-browser",fa: "\/lookup\/doi\/10.1136\/medhum-2019-011766?__cf_chl_f_tk=GxbLfn7qqd5HCJUpKYm13HQb6yY7fDdyhPKSVzFndKM-1739899738-1.0.1.1-UWGVEgw22ufGK04yI.jmlzKyMSBIwFPxU3kgZQSuquY",md: "av5nS3xUugUdvrn_3YlLo7YgnAupMGVNg2z086fffZs-1739899738-1.2.1.1-9Rr9dIuu_0r9v9A0.4FGor6iNvQJX3y5zBewwS.6.oWone4YLqcvXghFkYCKVhNzMPp7VMKnwQfcXxipAAT7465tpTP2PycRS2BaOI5Enp47IZjL28usBIpGF0j8RF6ys6YrmR5YiK4ufYdwfXAkR8EWeM9uVY61P5D3GkaHCYoRkJnlcIbgIg8BSzzA_yLOH_qD5pNbs3eV3ouveXLhIRwCAHYdYiaVB23lp7x37egm0qxGV4L9I_etQ7SqlFbQ6IQPQkhK2tomqHBg3jj_2SH1VnuS1W_wQp5pnxr8FvQP3G7aqB1bCIxbgVEEUQmvQiaGCrgeeCnaG8ra6FbY_sBRmdYxvlst_IojqJo.IYBltAkjh3tpfSlTm59Spv1kRwpSAS3ZCPwif4rSaJilaGo56FJtKwrlliOSXYjDwE_w4VKNfnsie1skJk9FRCoOe2icJpHEAYGshKAmVqavvShLPYRQoeH8Q4G_z8xI1p2PktWe_s8.ot0MDK0plhVEVgpEe0gvN6.QuOXgQlWWY7NqjF2b0ZJ2qJTPHlOU_fSGpFlfD336l9H.83O4mvRCcTjLYs0sERuD5SGNWj2ncoNiT_fYINSnevOdK9QB7xxdcwlG7D7mww_Svq4eb7CGchZTv0twHhzyZKTnVbsYh1kYUKoSIWhWWzPP6IedsqsX8XinN0HkB52HUvdMI4SzOTveQt5JpTEUqiekXWdxQXownGWyCuJlNYe_2aJiMN4cnRLebYlOcNI67Vq9e8SBsTNvoZtfrr_1E7hczVLQRyoNnSFiYr_QS4YSkiZY9x1OYevW6Ws9avyxXJaEfmh6p4EuwUrgrszsJVcd_D.KsMfMVUJfdjwxoRJ17SAQeIQWwt7ptdePoZ_PQt1JZh0PJZsf1DmMHUQ2pMJt3v4TM6XrENgvrcEI7.US9kfzMJhPl_ZcrAXZiHLdBmfAyNM.bT9A0pakNEysdMlJIeLlDUa67CDtZvYwedbS9DMFv_Eqtgk_4kc0TF9b5vjuqsIQC_nzV1JMpsWMvh1UID01hE7Mi70RAX0TMqpQGAbph381SGKiMqYiGzw0vsdi_ouiojgw0WehX7f_JDtsKs0aoLlLPEJBktxlbiGO9BIrbfUAIc0A3QiIcAC4UvMX01sRCcCLfECED3rC2YVBnFmg2E4HJfyAuQrsSKSDMCL5ubIYhgcrBWCo.jnBau8XmikzYZjMolad0CyY95PCaOmpCZ4m_xP.SObxwMBu5Lto06sO8.uJfJ5Y_6mhCoPQ2wgYUyZxttJNk3e.eJGQ2CHWNUOmZT7qJiJQ403zM49eIa3xYLLenXe8dObWitH1LFQZ8ICKwaeNYgabDYO5eevZXKZJFCbWETToZuHSvBN0eUna1AvWlvYy5KHwwwVv_WQdJrhvcIgiVEtcsyLJPo77FQNXDPCv7kpEgyMa9ic3cFp2An5qtEPEjUjKmnllksbrlFsN5DzCMtNFWSb7teESuP3UYJsl.kO9D9Z.6InKM.WNOyjLVQ3sjp4K34vksQqnZAHAHiaeE_kSEMSJfXwBhHjW9E3BDHJD.Icp8rWmjr9YQ4x8tM7UXDxoGuhwy7xGoeYA28cKeJ1rodCKx7TLDyx89vJr0Kvt2yqXJAYRhOKyMuU.B.XLHre2aQ3PaE0BuPnvKL_8XhwdmFo2ztMJk4G5F5m2vdzyrGCyU.etdvU4eBscozevElo9y.kt3sc.dmYkix5dvgYerO_S4n9ei3Hy6mDJy1S6w4bljNgDEnIibvKD8x3DXdKDLBa66MsyiYlDBffQPatmms3R5el5MfxQZWSRYp8Z82zFrSCw9wziCg60Mm1qlERGiAgEMEjWGqCCVXR8trI9ufw.FIGjIaP2hoKTlhzQNQ58vQ4vhyV8GwPBloSDd_g5rQiOgd8REoTj_BCFZUEuKlBdqAX4uZ2kgsqXsWRj6Mb6SseY90.IT5YbvcuninYMEtNA7KXh_Ahq3qz5srK5E_RXacSYwM2ryFdY5Ni6En5_GJR0Ihrk6N4ZUagKPD9aEAWQfgI0FklUqbQ5CtUHQzpxbIrXCB182cnP3iNc0qpnT3juZ2SULdosqVQ.LB2ygTwKmnnoZWrC4jVJHp8JMprSCNlo9VCmOSDJh29TNbyHzV8cWkFAKjtpZhNqWR2BClGEC0adH6dNwygw54GCFNd5ehaE8MMAIJgvelrc2kIFriHI65d3hVc.VvtZZj_5odCSd.o285csW7tG9z2Jgkh7shqFs9R5TdTGnbYhasz.HghoXRcVYs3zwuI5vSzUZTr15hs8uAfQkqDMsKcPdF3urQgM2vX6utVTgkjyym0djFllEkmF73jrqcskiobdNY0nc3M.YqFV4tCcZuDwdDLgwFIMPvxLkmvOA49AvGdXjGa7b3BVK703lll1_YwARLTjs333W.ci9P4Kn_3UqC.O1l2T2PWO6ubJibiEPckwgy1eeI9dmF8vuboQmkGo_7u6B60y193JVDca6GpyXrv7fraS_b_Fajz4NXc89ryBrBQVKL6FNVKl6nGfLaFUQlKxnd3D",mdrd: "DwKjwaXVXzgKfCw7MuDcvE2rpT1Q6wAnwriUPj5V19w-1739899738-1.2.1.1-gJZ2YcUSzjUaskmDVmrMmUAtpIQRp5xrW.R5gBDVsHeUjPwl4Pe8utK0h6O3UicWSW.iznyTOZXyIr3mRfEaZ_rWpecfTtVToMNLhOFq0GZEQi770lXiDEr7dx56xWI7VAncm5nJxCoT5.B9Iz1Icl2Awp8JARCSpxxz3XpPGuJ3FSFwDXgLGhEHQaMCERQ3J6njMQlqjgERPoSHlRjnfI2_GuANtor.Hr5SErju60KTlpoggQcoS8MtbCmMVTkv1s2dy0ZOxxVBqj3YtPi7Gkl.fUwVHWKlA.eJjLEM00c5nW2o8S.XpTNg7hkpZFcRU6OydKTf5_qfEdinPL98eU.ZlEBq4FScf.9.GpWqP6JasEDfkBMolpaaXeZ1t1wAWTsWuokX9_NgL4XoOAt73V1F054XJGuRS88KhyPrxWWc4BY3WOIwYg6zsdqPNPOGF4jijYoUp0990xwhkjHDiXIgX.0FGA2ZBUsrIduz8mD_gn6xAJSogOgrM4Thrpxi7ElmBUqlwZxLXYvLwH5OBWp9g39uUf4wmI1EnjqChrx8OVxF9Oe2vBK0mcnYT3HaXnktMpvHf6z46n9_nYLuxJhbUiUxXiE7ScFYGbqzJK6XO6rgoB_wGMMnf4rOXn.ARCYfi6ykSB6K569wtAYwXEGKFSwWFcD88Tu5yqV2mTkEj6gPbOmYqgG6TpdvX4YgeUQCM.BgTv4SzVouuHr1N4b_sVPzjb6NhqNAHIBZ_EbdzPDZ9Ib2Cd8phlAepNXAIlsAz9P4ND_NSOosSOKGKb_76mxxKeq8QopGGF69lELq4.Y0ojlXskDpM9NnFt2Iab8BykLVXSBactEobHCljQQXC7_neXxAR8r4jd83XBB5y5Nb.AwZo6dVgpgEkVZ2prYbt6Q35C1h.fQXaxf_aPW2X7mlzrQsnOqMd91EHn4Zmn.GVUOZRH0H7CLQLfrrn09LGAsgr1ML1GjqMIcrhNBCKdnroAfPtcT9ZIaLuCewtTGbNEhGn.GPgZh4lPTZ3nY9eb_IafuVmknmTjZsIK7Ex87MVbO6C4FvQPucb_AEv_lzJm0NO_2_TG3S5VbbyJ2mawgFajYp9.xRZPz7uiHJIgw9eQZ1jdK106odNRzX5f11fq.nJTIZDjK9YSF2E_tMftUPLD52HgyK5TG_MkL1relzozsAsKoc4qW9KKsWeOqnPRzbgUu7gdY9agrrOcQsETtloAq3bTaDm1HizCOYvrLNRwwqIt3JAFpE2mqQ5WHAZAQXazkoWCJSBgqo3N1p8bCDjWaShFZrCXme.SACxz6u5AXuL9CHo6.kPwtCtXN6FRQ7RqpkNwk6lWB51pZ2E88bgCcA4nzNNY3A8pE1TNyuKfP2lNrVmNXcLfqnlI2keU6XPr.f2oK3rlWzI5Ls_i3fXHHzo1yuyW2jdGTYRFjWlqn.kxdgBbT26PM5zCjqzSEPuq_IA6o1_NmSwl_h10JCcuDnp_etD9WkDUy4NaJioFQglcszB4fQbQPLe3akXO.372ZtrfFgFuI2wwde9g9uVhLt1.n.DUu2UmFjc83aI15aEN9Y4OHwpZ_6QKabVkA1cq8d5HR46ADrk2GJHGZPQqg7dK1QgeNlS7NhzR.s4avwOl9B_0elaJFUPSLx2DJHUNwz09mGPWduYB71S3Z3sm0vvs7QAGQs9.Byih2bmBx8P9j.Inby4MVoeMBTSwEGBhOrblH48JivFsEzp.e909goIAWNsYHg5otIBEAvio9h32ZfomgKADp8xMY5CAGytIJk5geJR0xVN6xMy8SIqRPXjd5Bql0VcEMHy1gN0ed_TDOdhbSDZY.CQ1uaezZ2YaSAYvDHgY6VRz.UrYpf3S0sqZvz.AKliYA4I5x_wsSVt5pAQvMewgBQoKsx5DcT0FFvpq8K12hLF4Z2T8Gxat220ND7lBv_XrvPuMAtOBANHLmsxdHAX5ggfs4UL7hQ_AyYIV1xQ4eV"};var cpo = document.createElement('script');cpo.src = '/cdn-cgi/challenge-platform/h/g/orchestrate/chl_page/v1?ray=913fbc95f9758333';window._cf_chl_opt.cOgUHash = location.hash === '' && location.href.indexOf('#') !== -1 ? '#' : location.hash;window._cf_chl_opt.cOgUQuery = location.search === '' && location.href.slice(0, location.href.length - window._cf_chl_opt.cOgUHash.length).indexOf('?') !== -1 ? '?' : location.search;if (window.history && window.history.replaceState) {var ogU = location.pathname + window._cf_chl_opt.cOgUQuery + window._cf_chl_opt.cOgUHash;history.replaceState(null, null, "\/lookup\/doi\/10.1136\/medhum-2019-011766?__cf_chl_rt_tk=GxbLfn7qqd5HCJUpKYm13HQb6yY7fDdyhPKSVzFndKM-1739899738-1.0.1.1-UWGVEgw22ufGK04yI.jmlzKyMSBIwFPxU3kgZQSuquY" + window._cf_chl_opt.cOgUHash);cpo.onload = function() {history.replaceState(null, null, ogU);}}document.getElementsByTagName('head')[0].appendChild(cpo);}());</script></body></html>