The vast majority of cases of malaria diagnosed in the UK occur in people who have been infected abroad. Occasionally however, cases of malaria are reported in the UK where the route of acquisition is not immediately apparent from an explanatory travel history. These cases are termed 'cryptic'. Cryptic malaria occurs very infrequently. Since 2002, only seven cases of malaria, caused by P. falciparum, have been identified that had no explanatory travel history. On investigation, these were classified as probable airport malaria (one), possible baggage malaria (two), nosocomial transmission (one known and one probable) , transfusion (one) and one has remained unexplained. (See guidance document below for more information about cryptic malaria classifications).
Cryptic malaria cases require investigation primarily to explore possible routes of transmission that may have public health significance within the UK. For example, person-to-person transmission in a health care setting or from a blood transfusion (induced malaria) would require public health investigation and intervention. Similarly, although considered to be very unlikely in current climatic conditions, the possibility of introduced malaria (the first generation of malaria, where the mosquito was infected from an imported case) or indigenous malaria (the second generation of malaria, where the mosquito was infected by biting an introduced case) would also have public health implications.
This page aims to assist health professionals with the initial investigation and classification of cases of malaria in the UK where the route of transmission is unclear or unusual. It defines various classes of cryptic malaria, outlines a protocol with a questionnaire tool for initial investigation and discusses inter-organisation communication issues and responsibilities around such cases.
Last reviewed: 3 February 2011