International and Tropical Department, Institut de Veille
Sanitaire, Saint-Maurice, France
We report a situation update of imported chinkungunya infections in metropolitan
France (the part of France that is in Europe, including the Mediterranean
island of Corsica), from April 2005 to June 2006 .
Since the beginning of the epidemic in March 2005, 266 000 cases of chikungunya
fever are estimated to have occurred on the island of Reunion, a French
overseas territory . Weekly estimates of suspect cases are based on the
number of patients with suspected chikungunya seen by sentinel physicians
on the island of Reunion and extrapolation of these figures to the entire
island population. Numbers of newly estimated cases peaked at 45 000 in
week 5 (first week of February 2006), and have since decreased. By June
2006, the estimated weekly number of cases was around 400. The islands of
the southwest Indian Ocean (including Comoros, Madagascar, Mauritius, Mayotte,
and Seychelles), and several states of India  have been affected by chikungunya
epidemics in 2005-2006.
Imported cases of chikungunya have been reported from several European
countries . The vector, responsible for the transmission in the French
territories of the Indian Ocean is known to be Aedes albopictus.
This mosquito has been detected on the French Mediterranean coast, between
the cities of Menton and Nice, and recently in the Bastia area of Corsica,
a French Mediterranean island.
Given the situation and the high number of travellers (304 113 for the
year 2004 according to the French Ministry of Tourism) between Reunion and
metropolitan France, surveillance of imported cases and vector densities
is an important part of the risk assessment of autochthonous transmission
Chikungunya serological testing in France is carried out by two national
reference centres for arboviral diseases and two private laboratories.
Data on positive tests were collected regularly between April 2005 and
June 2006 and have been analysed. The variables used are patient and laboratory
postcodes, age, sex and date of blood sampling. An imported case is defined
||Detection of IgM antibodies against chikungunya virus and/or detection
of viral RNA by PCR, and/or positive viral culture;
||Sampled in metropolitan France (even if the patient is not resident
in metropolitan France).
From April 2005 to June 2006 inclusive, 766 imported cases of chikungunya
were identified in metropolitan France. The mean age was 48 years (range:
5 months-83 years), and the male:female sex ratio was 0.9:1.
The temporal evolution of imported cases correlates with the dynamics of
the epidemic in Reunion (Figure 1). Between April and July 2005, an average
of 20 imported cases was observed monthly, corresponding to the first Reunion
outbreak peak and the epidemics on the Comoros islands. Following a decrease
between August and November 2005 (winter in the southern hemisphere), the
estimated number of cases increased again and peaked in March 2006 (177
imported chikungunya cases).
Since then the trend has been decreasing, with 119 imported cases reported
in April, 88 in May and 48 in June. No severe chikungunya cases (neurological
signs and/or organ failure) were reported in metropolitan France between
April 2005 to June 2006.
Figure 1. Chikungunya: Imported cases to metropolitan
France and estimated cases in Reunion (Reunion data source: Cellule Inter
Regionale d’épidémiologie Reunion-Mayotte)
Cases were documented in most areas of France (Figure 2), but were concentrated
in the greater metropolitan areas of Marseille, Lyon and Paris.
Figure 2. Geographical distribution of imported cases
of chikungunya in metropolitan France, April 2005-June 2006
The number of chikungunya cases imported to metropolitan France has been
decreasing since March 2006. This temporal evolution correlates with the
dynamics of the epidemic in Reunion, which has also been going down. The
peak of the imported cases in March 2006 was observed one month later than
the peak of the Reunion outbreak, which occurred in February 2006. This
time lapse may be explained by the different methods used: distribution
of estimated cases in Reunion was based on clinical symptoms onset, while
imported cases were dated by blood sampling, which was often done several
days or even weeks after symptom onset.
The number of imported cases is probably underestimated, since asymptomatic
cases cannot be detected by surveillance. Chikungunya IgM antibodies appear
5 days after the onset of clinical symptoms on average, and can last for
several weeks. Having measurable IgM titres at a given time does not imply
viraemia, and only viraemic patients can cause further transmission. The
risk of secondary transmission in metropolitan French areas where the vector
is present is therefore probably overestimated, based on imported case data.
A. albopictus is known to be currently spreading around the world
, and is present in north and central Italy  and Albania. The mosquito
can transmit the virus, but its actual vectorial capacity (environment-dependent)
in metropolitan France is not yet well documented. A. albopictus
is also capable of transmitting dengue fever.
Risk assessment of autochthonous transmission is based on surveillance
of both the vector and imported viraemic cases. A plan for preventing the
circulation of chikungunya in metropolitan France  has been developed,
and reinforces entomological and epidemiological surveillance. Since 7 July
2006, chikungunya and dengue fever have been added to the list of diseases
for mandatory notification in France. Entomological surveillance in France
has confirmed the presence of the vector in the city of Bastia in northern
Corsica, in addition to the area on the southeast coast of France where
it had previously been identified. Alert procedures have been developed
and coordination with vector control services strengthened. All ‘suspect’
chikungunya cases detected in these regions with confirmed vector presence
must now to be reported immediately, without waiting for biological confirmation.
This should facilitate rapid information to the surveillance system and
the implementation of control measures.