Epidemiological update: Legionnaires’ disease cases associated with travel to Dubai, 03 August 2017

Increase in travel-associated Legionnaires’ disease among European travellers returning from Dubai since 1 October 2016

The ECDC surveillance scheme (ELDSNet) for travel-associated Legionnaires’ disease [1] has observed an increase in the number of cases associated with travel to Dubai, United Arab Emirates, since the beginning of the last quarter of 2016 compared with 2014–2015 (Figure 1). Case numbers reported in February, April and May 2017 continue to be significantly above the level observed in recent years. This epidemiological update is the sixth since a rapid risk assessment was published by ECDC on 23 December 2016.

Figure 1. Distribution of Legionnaires’ disease cases associated with a stay in Dubai, United Arab Emirates, by month of illness onset, EU/EFTA countries, January 2014 to May 2017, as of 1 August 2017

Note: Five cases with onset in June and July 2017 were excluded from the graph because of reporting delays that do not allow comparison with previous years. Cases associated with private accommodations are also excluded.

As of 1 August 2017, 72 cases of travel-associated Legionnaires’ disease with a history of visit to Dubai within 2–10 days prior to illness and with onset since 1 October 2016, have been reported to ECDC by EU Member States and one EFTA country. The most recent case has a date of illness onset of 18 July 2017.

Cases were reported by the United Kingdom (34 cases), Sweden (8), Germany (7), France (6), the Netherlands (6), Denmark (4), Austria (1), Belgium (1), the Czech Republic (1), Hungary (1), Ireland (1), Spain (1) and Switzerland (1). The delay between week of illness onset and the actual report date to ELDSNet is around two weeks, ranging from one to six weeks. Therefore, the number of cases reported in the past six weeks is likely to be underestimated.

Figure 2. Travel-associated Legionnaires’ disease: distribution of cases with a history of stay in Dubai, United Arab Emirates, by week of onset and accommodation site clustering, weeks 37/2016–29/2017, reported as of 1 August 2017 (n=72)

Of the 72 reported cases with disease onset since 1 October 2016, 65 used commercial accommodation sites (hotels or apartments) and seven used private accommodation sites. Twenty-one cases used a hotel that was associated with another case falling ill since 1 October 2016 (Figure 2). Sixteen cases stayed at an accommodation in another location in the United Arab Emirates or in a country other than their home country during their incubation period. Two cases were reported as fatal. Fifteen cases stayed in Dubai during the entire duration of their incubation period.

All cases are laboratory confirmed. Five of the cases had their infection further characterised as Legionella pneumophila serogroup 1 sequence base type 616 and one as Legionella pneumophila serogroup 1 sequence base type 2382. Sequence base type 616 is uncommon in Europe and has been associated with other Legionnaires’ disease cases returning from Dubai in previous years. Sequence base type 2382 is a new sequence type closely-related to type 616 (personal communication, ELDSNet network). Two cases had their infection strains characterised as Legionella pneumophila serogroup 2-14 sequence base type 1327.

Environmental investigations

Public health authorities in the United Arab Emirates have informed ECDC that environmental investigations were undertaken at the notified hotels and Legionella count results showed acceptable levels for water systems (hot and cold water should not exceed 1000 cfu/litre) [2]. This threshold level is the same as used to determine action levels in the European technical guidelines [3].

According to United Arab Emirates authorities, risk assessment of accommodation sites notified by ELDSNet and of possible high-risk sites such as cooling plants and major fountains has been undertaken in Dubai. To date, no single source of infection has been identified. It is also reported that Dubai Municipality has undertaken supplementary water sampling, investigates new cases notified by ELDSNet and monitors the situation in accordance with Dubai laws and regulations.

ECDC threat assessment for the EU

The majority of reported cases are associated with different accommodation sites dispersed geographically across Dubai, suggesting a common source not associated with accommodation sites.

The assessment outlined in the rapid risk assessment published on 23 December 2016 has not changed, since cases have continued to be reported with illness onset in recent weeks above the level observed in previous years. Its recommendations remain valid, in particular:

• to inform travellers − particularly those above 50 years of age, smokers and immunocompromised persons − to seek medical advice if they experience respiratory infection symptoms up to two weeks after travelling to Dubai to ensure early diagnosis and treatment.
• Remind clinicians to consider Legionnaires’ disease in patients presenting with community-acquired atypical pneumonia with a history of travel to Dubai or the United Arab Emirates in the two weeks prior to disease onset.

References

1. European Centre for Disease Prevention and Control. European Legionnaires’ Disease Surveillance Network (ELDSNet) − Operating procedures. Stockholm: ECDC; 2012. 
2. Dubai Municipality, Public Health and Safety Department. Guidelines for the control of Legionella in water systems – Rev. 2, June 2010. Dubai: Public Health and Safety Department; 2010.
3. European Guidelines Working Group. European technical guidelines for the prevention, control and investigation of infections caused by Legionella species – June 2017.