Rapid Risk Assessment: Clusters of autochthonous chikungunya cases in Italy

risk assessment
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European Centre for Disease Prevention and Control. Clusters of autochthonous chikungunya cases in Italy, 14 September 2017. Stockholm: ECDC; 2017.

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Two related clusters involving autochthonous transmission of chikungunya virus have been detected in the cities of Anzio and Rome, two areas located 60 km apart in the Lazio region of Italy. Transmission of this type, in areas where Aedes albopictus mosquitoes are established and at a time when environmental conditions are suitable for increased mosquito abundance and activity, is not unexpected. This event is the second introduction of chikungunya local transmission in Italy resulting in an outbreak, following a previous outbreak in the Emilia-Romagna region in 2007. Other autochthonous transmission events were detected in France in 2010, 2014 and 2017.

Executive summary

Two related clusters involving autochthonous transmission of chikungunya virus have been detected in the cities of Anzio and Rome, two areas located 60 km apart in the Lazio region of Italy. Transmission of this type, in areas where Aedes albopictus mosquitoes are established and at a time when environmental conditions are suitable for increased mosquito abundance and activity, is not unexpected. This event is the second introduction of chikungunya local transmission in Italy resulting in an outbreak, following a previous outbreak in the Emilia-Romagna region in 2007. Other autochthonous transmission events were detected in France in 2010, 2014 and 2017.

The fact that the first transmission event is estimated to have taken place around mid-July 2017 or before, that cases have been reported in two separate areas, and that several additional symptomatic cases are being investigated suggests that local transmission has been effective in spreading the disease. As a consequence, more cases are expected to be identified in the near future. Given that environmental conditions in the area are expected to remain similar in the coming weeks, the likelihood of further transmission in the Lazio region is high.

Early detection of imported cases is critical to prevent establishment of local transmission following the introduction of the chikungunya virus by a viraemic traveller to an area where Aedes albopictus is established. Early detection of imported cases during the season of high mosquito activity in areas where Aedes albopictus is established relies on increased awareness among clinicians and travellers returning from areas with chikungunya transmission, combined with appropriate laboratory detection capacity.

The detection of an autochthonous case should trigger epidemiological and entomological investigations to assess the potential of onward transmission and guide vector control measures aimed at lowering mosquito population density. Member States should consider reporting any confirmed case of chikungunya having travelled to Italy in the two weeks preceding the onset of symptoms to the Italian health authorities. This might help identify possible additional transmission foci around the affected area.

In addition to coordinated vector control activities, community sensitisation around transmission foci is important in order to inform people of the need for personal protection measures against mosquito bites and to engage local communities in the elimination of mosquito breeding sites. Personal protective measures to reduce the risk of mosquito bites include the use of mosquito repellent in accordance with the instructions indicated on the product label; wearing long-sleeved shirts and long trousers, especially during the daytime when Aedes albopictus mosquitoes are most active; sleeping and resting in screened or air-conditioned rooms and using mosquito bed nets at night and during the day.

Travellers returning from areas where chikungunya transmission occurs should be advised to seek medical attention if presenting with symptoms compatible with chikungunya virus disease in the first two weeks after return, particularly if returning to areas where Aedes albopictus mosquito is established. This will help reduce the risk of further local transmission. The application of personal protective measures against Aedes mosquito bites by travellers in chikungunya-endemic areas remains a critical factor for preventing the introduction of the virus into EU areas with established Aedes-competent vectors and suitable conditions for transmission.

Member States should consider the following measures to prevent the transmission of chikungunya through substances of human origin (SoHO):

  • excluding donations from travellers returning from affected areas in Italy;
  • temporarily interrupting donations in affected areas in the absence of validated and authorised nucleic acid testing (NAT) for the screening of donors;
  • deferring donors diagnosed with chikungunya for at least four weeks after the resolution of symptoms, as suggested by data available on viraemia during and after chikungunya infection;
  • applying effective pathogen inactivation for the apheresis collection of platelets and plasma in affected areas;
  • reminding donors to report symptoms after donation in areas infested by Aedes albopictus;
  • consulting a transplant infectious disease expert before considering organ donation from donors infected with chikungunya virus.

The SoHO safety measures should be applied at a geographical level that takes into account the estimated extent of transmission and the daytime movements of the local population from the affected neighbourhood. At the moment, the municipality of Anzio is considered to be an affected area and SoHO safety measures should be applied locally.

Preparedness regarding chikungunya in the EU requires the capacity to detect cases in areas where the competent vectors are present; strengthened surveillance systems (including clinician awareness, laboratory capacity for confirmation and rapid notification of cases); regular review of contingency plans for mosquito-borne outbreaks; education and cooperation of the general public on how to control mosquito breeding sites; strengthened vector surveillance systems and rapid implementation of vector control measures following each case.

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