Increasing impact of Bali travel on infectious disease notifications in Western Australia
From 2006 to 2012, the number of people flying from Western Australia (WA) to Bali increased more than 6-fold, while the proportion of WA trips destined for Bali rose from 7% to 24%. In 2012 there were more than 400 000 people on flights to Bali from WA, from a resident population of 2.4 million.
Impact on disease notifications
For most diseases, the Western Australian Notifiable Infectious Disease Database records travel details only to the country (e.g. Indonesia), not to the regional level. However, nearly all Indonesian-acquired infections are likely to be from Bali, given that 93% of travellers to Indonesia in the period from 2006 to 2012 flew to Bali.In line with increased numbers of Western Australians flying to Bali, the number of Indonesian-acquired notifiable disease cases also increased 6-fold from 2006 to 2012 (173 to 1069 cases, respectively), and the proportion of overseas-acquired cases attributed to infection in Indonesia increased from 10% to 29% of cases (Figure 1).
Figure 1 – Number of notifiable disease cases reported in Western Australia that were acquired
in Indonesia and other countries, and Bali travel population from WA, 2006 to 2012
From 2006 to 2012 the notifiable diseases on which Bali travel had the greatest impact were dengue fever and Salmonella infection.
From 2006 to 2012, there was a 46-fold increase in the number of Indonesian-acquired cases of dengue fever (9 and 415 cases, respectively) and the proportion of all dengue fever cases notified in WA that were acquired in Indonesia increased from 56% to 80%. In 2012, 40% of all notified Indonesian-acquired infections were dengue fever (Figure 2).
Figure 2 – Indonesian-acquired notifiable infectious diseases in Western Australians by disease, 2012
The number of notified Salmonella infections acquired in Indonesia increased 9-fold (from 28 to 266) from 2006 to 2012, and the proportion of all Salmonella cases notified in WA that were acquired in Indonesia rose from 4% to 23%. In 2012, 25% of Indonesian-acquired notifiable diseases were Salmonella infections. For both dengue fever and Salmonella, the increase in case numbers from 2006 to 2012 was greater than expected based on the 6-fold increase in Bali travel population. This suggests that during this period the risk of transmission in Bali also increased for both diseases. This could reflect changes in local factors in Bali, such as a decline in food safety standards and increased dengue virus transmission, and/or greater risk-taking by WA travellers.
Other diseases which comprised more than 5% of Indonesian-acquired cases in 2012 were Campylobacter and Chlamydia infections (157 and 95 cases respectively), but for these diseases the increase in notifications from 2006 to 2012 (4.2 and 3.8 fold, respectively) was less than expected based on the increased Bali travel population. In addition to dengue fever, salmonellosis, campylobacterisosis and chlamydia, in 2012 there were 10 or more Indonesian-acquired notifications for each of gonorrhoea (n=37), Cryptosporidium infection (n=14), and Rickettsial infections (n=10), primarily murine typhus. Other less commonly acquired notifiable infectious diseases included syphilis, typhoid fever, hepatitis A,chikungunya and Legionnaires’ disease.
An additional and very significant impact of increased Bali travel has been the provision of rabies post-exposure prophylaxis to people reporting bites or scratches from local animals, mostly monkeys, but including dogs. Since 2008, 536 people have been provided with prophylaxis, 157 of these in 2012. This normally requires an expensive course comprising administration of both human rabies immunoglobulin and several doses of rabies vaccine, even if the course has been commenced in Bali prior to departure.
Conclusions and recommendations
The main notifiable infectious disease risks for travellers to Bali are from mosquito-borne, gastrointestinal and sexually transmitted infections. WA travellers need to be more aware of these risks and take appropriate precautions to prevent infection. In addition to travel vaccination recommendations, pre-travel advice should include information on preventing mosquito bites, diarrhoeal diseases and sexually transmitted infections.
Mosquito bites can be prevented by:
- applying insect repellents containing diethyl toluamide (DEET) or picaridin
- wearing long, loose-fitting, light-coloured protective clothing
- sleeping in screened accommodation or using bed nets.
People travelling to Bali and other dengue-affected areas should be aware that the mosquito that transmits dengue fever commonly bites during the day and in shady, indoor situations.
Diarrhoeal diseases, can be prevented by:
- not consuming foods or drinks purchased from street vendors or other places where conditions may be unhygienic
- not eating raw or undercooked meat and seafood
- not eating undercooked eggs
- not eating raw fruits (e.g., oranges, bananas, avocados) and vegetables unless the traveller peels them
- not drinking tap water, ice or unpasteurised milk. Safe beverages include bottled carbonated beverages, hot tea or coffee, beer, wine, and water boiled or appropriately treated with iodine or chlorine.
Sexually transmitted infections can be prevented by practising safe sex and always using a condom and lubricant with any casual sexual partners.