. 2003 Jul 15;33(7):912–920. doi: 10.1046/j.1365-2222.2003.01715.x
This article is being made freely available through PubMed Central as part of the COVID-19 public health emergency response. It can be used for unrestricted research re-use and analysis in any form or by any means with acknowledgement of the original source, for the duration of the public health emergency.