Between 1987 and 2006, 39
300 cases of malaria were reported to the Malaria Reference Laboratory. Data were largely complete for central variables (age 96%, sex 94%, date of diagnosis 98%, outcome 99%) but less complete for some supplementary information (country of visit 88%, purpose of travel 71%, country of birth 64%, prophylaxis use 62%). The median age of cases was 31 years, and 38% were female. Malaria was attributable to a single species in 98.7% of cases: P falciparum
859 (63%) cases, P vivax
904 (28%), P ovale
6%, P malariae
1.5%, and one case of P knowlesi
. Table 1 shows mortality by species and time period.
Table 1 Reported cases of malaria and deaths from Plasmodium falciparum malaria, 1987-2006
The pattern of malaria species has changed markedly over the study period. Reports of P falciparum increased through the study period (linear regression: β=+27.4 notifications/year, P<0.0001); increases for P ovale and P malariae were less pronounced. In contrast, reports of P vivax declined over the study period (linear regression: β=−36.2 notifications/year, P<0.0001) (fig 1). The ratio of P falciparum to P vivax infections increased from 1.3:1 in 1987-91 to 5.4:1 in 2002-6. Table 2 shows region of travel where malaria was acquired, by species; 96% of falciparum malaria was acquired in Africa, whereas 80% of vivax malaria came from South Asia.
Fig 1Reported cases of malaria, 1987 to 2006
Table 2 Reported cases of malaria 1987-2006, by global region visited (where reported*). Values are numbers (percentages)
Table 3 shows data on reason for travel. Where reason for travel was known, 20
488 cases, or 75% of imported cases, occurred in UK travellers (visitors from the UK to malarious countries); the remainder were among visitors to the UK. The number of journeys to malarious countries from the UK increased markedly (from 593
000 visits in 1987 to 2.6 million visits in 2004), but the median duration of visits to malarious areas of cases decreased (1987-91, 42 days; 1992-6, 35 days; 1997-2001, 28 days; 2002-6, 28 days). Of the UK travellers whose reason for travel was known, 13
215 (64.5%, 95% confidence interval 64% to 65%) had travelled to visit friends or relatives in their own or their families’ country of origin. Most, but not all, of these people were visiting countries where their family had some degree of ethnic origin. The risk of malaria per episode of travel from the UK decreased between 1987 and 2006 for all species of malaria, most notably for P vivax
Table 3 Purpose of travel among reported cases of malaria, 1987-2006 (where reported*)
Fig 2Risk of reported Plasmodium vivax per travel episode to regions endemic for malaria
Of the 34
359 cases with reported travel history, 24
599 (71.6%, 71% to 72%) occurred after travel to Africa; this included 20
774 of 21
541 (96.4%, 96% to 97%) cases of falciparum malaria. Sixty seven per cent of malaria in UK travellers arose after travel to west Africa; travel to Nigeria and Ghana accounted for 54% of all imported P falciparum
. Of those people who acquired malaria in west Africa, 76% were visiting friends or relatives in their own or their families’ country of origin, whereas tourism was the most common purpose of travel for people visiting southern Africa (48%) and east Africa (44%). People who made trips to visit family in Africa were significantly more likely to have acquired malaria than those travelling for other reasons (risk ratio of reports per 10
000 trips=3.65, 95% confidence interval 3.5 to 3.8; P<0.0001).
Travel to South Asia accounted for 8452 cases, 24.6%, (24% to 25%) of imported malaria, of which 92% was P vivax
. Over the study period, imported cases from this region declined significantly for all species of malaria despite a sustained increase in volume of travel. From 1987 to 1991, 3036 vivax cases arose from the Indian subcontinent, accounting for 31% of all UK malaria. By 2002-6, this had decreased to 705 cases (8% of all UK malaria). Of cases in which the purpose of travel was reported, 89% of UK travellers visiting South Asia had done so to visit family and friends. People travelling for this reason were at significantly higher risk of acquiring malaria than other travellers (risk ratio of reported cases per 10
000 trips=7.9, 7.2 to 8.6; χ2
Of UK travellers with complete records (17
129), only 42% reported taking any form of chemoprophylaxis against malaria during their period of travel. Significant differences existed in the use of chemoprophylaxis (including non-standard drugs) according to the geographical origin of cases (table 4), and people who had visited family in their country of origin were less likely to report the use of any prophylaxis than other travellers (Mantel-Haenszel odds ratio adjusted for age and sex=0.23, 95% confidence interval 0.20 to 0.25). Among reported cases in people who travelled to sub-Saharan Africa between 1999 and 2006, over which period consistent recommendations on prophylactic drugs for this region were made, only 7% of people visiting friends or relatives in their own or their families’ country of origin reported having used recommended drugs, compared with 24% of people travelling for other reasons (χ2
Table 4 Use of chemoprophylaxis* among travellers from UK, by region of birth place
Probably reflecting the distribution of first generation and second generation immigrant groups, a striking geographical distribution of cases occurs in the UK (table 5). Forty one per cent of all cases of malaria in the UK, and 65% of cases of P falciparum malaria, occurred in London residents or visitors to London, whereas most (68%) cases of P vivax were reported from other regions of the UK, notably the West Midlands (a region encompassing the densely populated conurbations of Birmingham, Wolverhampton, Coventry, and Stoke-on-Trent). The seasonality of P falciparum cases shows a bimodal pattern, with peaks in January and September, mirroring patterns of travel to destinations where transmission of P falciparum occurs throughout the year (fig 3). By contrast, patterns of monthly P vivax reporting show a single summer peak, paralleling the peak transmission periods of malaria in much of India and Pakistan.
Table 5 Reported malaria cases by UK region, 1987-2006*
Fig 3Calendar month of onset of reported malaria in the UK, 1987 to 2006
Mortality data show that 183 malaria related deaths occurred over the period of the study, giving an overall case fatality rate for P falciparum malaria of 7.4(95% confidence interval 6.3 to 8.5) per 1000 cases; we found no evidence of a significant change over the period of study. Case fatality was significantly lower among people travelling from the UK to visit friends or relatives in their own or their families’ country of origin than among people travelling for other reasons (0.25% v 1.9%; χ2=83.1, P<0.001).