Deferral criteria and testing strategies for dengue virus in blood donors returning from affected areas : survey results.
Date: 2025-08-08
Institutions: European Centre for Disease Prevention and Control
Subjects: European Economic Area, European Union, disease prevention, disease vector, health control, health risk, invasive species, risk management, substance of human origin, user guide, viral disease

ASSESSMENT 

Deferral criteria and testing strategies for 
dengue virus in blood donors returning from 
affected areas  

Survey results 

Key findings 

To support discussions with the ECDC network on substances of human origin (SoHO-Net), ECDC conducted a 
survey among members of the SoHO-Net blood group on the donor assessment and deferral strategies for blood 
donors in the European Union/European Economic Area (EU/EEA) countries with regard to dengue virus. This 
report presents the results of the survey. 

•

•

• While 91% of the responding EU/EEA countries have deferral criteria for blood donors returning from dengue-
endemic areas, only 55% have specific criteria for those returning from affected non-endemic areas within the
EU/EEA.
For countries that defer donors returning from endemic countries or affected areas in non-endemic countries,
the deferral period is consistently 28 days. For donors with a confirmed dengue diagnosis, the deferral period is
reported as 120 days.
Different trigger criteria are used to implement safety measures for prospective donors returning from affected
areas with local dengue outbreaks in EU countries. Five countries implement safety measures when there is at
least one locally-acquired case in an area with an active cluster of dengue, while six countries implement
measures on a case-by-case basis.
Deferral of prospective donors who have travelled to a dengue affected area is the most commonly used blood
safety measure for prevention of transfusion-transmitted dengue. Nucleic Acid Testing (NAT) for dengue is
rarely reported as a screening tool.
There is no standardised definition for the geographical scope of an ‘affected area’ for local dengue outbreaks in
EU countries, with risk levels being applied at the country, regional, or municipal level by different Member States.

•

•

Conclusions: The increasing frequency and size of autochthonous dengue outbreaks in EU/EEA countries 
presents an emerging challenge for blood safety. Safety measures reported by EU/EEA countries generally 
address travellers returning from endemic countries outside the EU and only a few countries report measures for 
travellers returning from affected areas in non-endemic countries.  

Suggested citation: European Centre for Disease Prevention and Control. Deferral criteria and testing strategies for dengue 
virus in blood donors returning from affected areas – survey results. Stockholm: ECDC; 2025. 

Stockholm, August 2025 
ISBN: 978-92-9498-815-7 TQ: 01-25-045-EN-N DOI: 10.2900/4266554 
© European Centre for Disease Prevention and Control, 2025. Reproduction is authorised, provided the source is 
acknowledged. 

Deferral criteria and testing strategies for dengue virus in blood donors returning from affected areas  

ECDC ASSESSMENT 

Introduction 

Dengue virus (DENV) is an enveloped, single-stranded, positive RNA virus belonging to the Flaviviridae family, 
within the Flavivirus genus. There are four distinct serotypes of DENV (DENV-1, DENV-2, DENV-3, and DENV-4), 
each capable of causing the full spectrum of dengue. The virus is primarily transmitted to humans through the 
bite of infected female Aedes mosquitoes, particularly Aedes aegypti and Aedes albopictus [1]. In addition to the 
vectorial route, DENV can also be transmitted through perinatal transmission [2], blood transfusion [3], stem cell 
transplantation [4], organ transplantation [5], and needlestick injuries [6]. Probable sexual transmission of DENV 
has also been documented [7]. 

The clinical manifestations of dengue range from mild, asymptomatic infections to severe and potentially life-
threatening conditions. It is reported that 60–80% of individuals infected with DENV will remain asymptomatic 
[8]. However, this proportion can vary widely across studies due to the impact of prior infections on the 
likelihood of severe dengue, as well as differences in methodological aspects [9]. The definition of 
‘asymptomatic’ seems to be one key aspect for this variation. In a systematic review of the asymptomatic 
dengue infection rate, authors reclassified asymptomatic infection into three groups, aiming for a more precise 
description of the cases included: no symptoms, subclinical (i.e. mild or aspecific symptoms), and unapparent 
(infections not captured by the healthcare system regardless of symptomatology). Rates of asymptomatic 
infection ranged from 0 to 42% of cases (median 7.5%, six studies) for the ‘no symptoms’ category; 0 to 100% 
of cases (median 64%, 30 studies) for the ‘subclinical’ category, and 50 to 100% of cases (median 72%, 14 
studies) for the ‘unapparent’ category [9]. 

In symptomatic cases, the incubation period typically lasts four to seven days (range: 3−10 days [10]), after which 
patients may experience a sudden onset of high fever, severe headache, retro-orbital pain, myalgia, arthralgia, and 
rash. In milder cases, these symptoms last from two to seven days. A subset of patients, approximately 2−5% [8], 
can progress to a more severe presentation after four to six days of illness. Severe dengue includes dengue 
haemorrhagic fever (DHF) and dengue shock syndrome (DSS), which are marked by plasma leakage, haemorrhage, 
circulatory collapse, and multi-organ failure. The exact mechanisms underlying the progression to severe dengue 
are not fully understood, but they appear to involve a combination of viral and host factors, including the host's 
immune response and genetic predisposition [1]. A median case fatality rate of 5% (range: 0−39%) was identified 
in a systematic review of observational studies analysing risk factors associated with mortality [11]. However, with 
good clinical management, the case fatality rate is below 0.5% [12]. 

The different dengue serotypes induce serotype-specific as well as serogroup-specific antigens. After infection, 
the adaptive immune response provides long-term immunity to the specific type and a shorter immunity to the 
other serotypes: between three months to two years, depending on reports [1]. Prior infection with a given 
serotype is thought to increase the likelihood of severe dengue after a new infection with a different serotype 
[13]. This increased severity is explained by antibody-dependent enhancement (ADE). The ADE model states 
that cross-reactive antibodies or sub-neutralising concentrations of serotype-specific antibodies bind and facilitate 
the entry of DENV through receptors on target cells, which include dendritic cells, macrophages, and monocytes 
[14]. Through facilitated entry, ADE is thought to increase viral replication in the early infection stage and 
increase the risk of progression to severe dengue, DHF or DSS. The management of the infection is based on 
symptomatic treatment and supportive therapies. To date, two vaccines against DENV have been authorised for 
use in the EU, both of which are recommended for use in dengue-endemic areas [12].  

The burden of dengue has been increasing worldwide in the past decade [15]. In 2024, over 14 million dengue 
cases and over 10 000 dengue-related deaths were reported globally [16]. Dengue is not endemic in mainland 
EU/EEA, and the vast majority of the cases reported in the EU/EEA are among travellers coming from dengue-
endemic areas. However, as competent vectors of DENV are established in mainland EU/EEA, local, sporadic 
outbreaks of autochthonous cases (locally-acquired cases) can occur, starting from an imported case. The 
frequency and size of these local outbreaks has increased over the last decade to events with outbreaks of over 
50 cases reported in 2022, 2023, and 2024 in France and Italy (Figure 1; [17]). This trend in increasing size and 
frequency of local outbreaks in mainland EU/EEA is expected to continue in coming years. Furthermore, with the 
geographical spread of competent vectors and longer periods of favourable environmental conditions for vector-
borne DENV transmissions across EU/EEA countries, such outbreaks could occur in an increasing number of 
countries in the future [18].  

2 

 
 
Deferral criteria and testing strategies for dengue virus in blood donors returning from affected areas  

ECDC ASSESSMENT 

Figure 1. Number of locally acquired dengue cases and outbreaks in the EU/EEA*, 2010−2024 (n=579)  

350

300

s
e
s
a
c

e
u
g
n
e
d

f
o

r
e
b
m
u
N

250

200

150

100

50

0

20

18

16

14

12

10

8

6

4

2

0

s
k
a
e
r
b
t
u
o

f
o

r
e
b
m
u
N

2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024

Croatia

France

Italy

Spain

Outbreaks

*EU outermost regions excluded

Source: European Centre for Disease prevention and Control, 2025 [17] 

The risk of transfusion-transmitted dengue  
Transfusion-transmission of dengue is well established [3], though the rate of transmission through transfusion 
of blood products from infected donors is uncertain, given the low number of reported transfusion cases, even in 
high-incidence areas [19]. A study reported a transmission rate from viraemic donors of around 30% [20]. 
Hypotheses for the low number of reported transfusion-transmission cases in endemic areas include undetected 
and unreported transmission events, which could be associated with misdiagnosis due to non-specific symptoms 
in recipients, mild disease manifestations in individuals infected through non-vectorial routes, presence of 
protective immunity in recipients in endemic areas, and co-transfusion of antibody-positive units neutralising the 
infectivity of viraemic donations [21-23]. In addition, in endemic areas recipients are simultaneously exposed to 
vectorial transmission (i.e. through mosquito bites) making it difficult to identify transfusion-transmission. 

Several studies among blood donors in endemic countries have documented viraemia in asymptomatic donors. A 
systematic review summarising the published DENV RNA prevalence among blood donors reported rates ranging 
from 0.0% to 5.5% in this population and a pooled viraemic rate of 0.2% [24]. In the three studies conducted in 
non-endemic countries (Australia 2008−2013, USA 2015, Portugal - date not specified), the viraemic rate was 
0.0%, with 0 positive NAT from 15 471 samples tested. A study conducted during an outbreak in Rio de Janeiro 
estimated the incidence of DENV infection in the donor population to be 6.2% (95% confidence interval [CI]: 
3.2%–9.1%) over the duration of the outbreak. Based on the increase in IgM-reactivity and the temporal yield of 
NAT, the authors estimated the viraemia remained detectable in individual donation nucleic acid tests (NAT) for a 
period of 9.1 days (95% CI: 4.4–13.9 days) after infection [25]. In this study, authors estimate that there was 
one RNA-positive donation per 800 clinical dengue cases in the general population of donor-age. 

3 

 
 
 
 
 
 
 
 
Deferral criteria and testing strategies for dengue virus in blood donors returning from affected areas  

ECDC ASSESSMENT 

A study conducted in Brazil (Rio de Janeiro and Recife) linked donor and recipient pairs and considered groups 
according to the presence of DENV RNA in the donation and the presence of DENV RNA in the recipients. The 
study describes six probable or possible 1 cases of transfusion-transmitted DENV, and 10 susceptible recipients 
who did not become infected by DENV despite receiving a DENV RNA-reactive blood component. The comparison 
of the viral load in the donations from both groups did not identify an association between transmission and viral 
load. A median viral load of approximately 200 copies/mL in the transfused blood unit was reported for both 
groups. No association with blood component type was found. Using blinded chart review to compare the 
probable and possible transfusion-transmitted cases to controls (transfusion recipients who had not received 
known RNA-positive components), the authors also reported similar rates of symptomatic infection among these 
two groups. No recipient developed severe dengue symptoms [20]. 

Assessment of blood donors for the risk of dengue virus in 
the EU/EEA 
Deferral of prospective blood donors (individuals presenting for blood donation) returning from dengue-endemic 
countries is a well-established safety measure by EU/EEA countries. The recent large outbreaks of dengue in certain EU 
Member States have led to concerns about the risk of transfusion-transmitted dengue from travellers returning from 
affected areas in the EU/EEA and raised questions on the appropriate safety measures for these travellers.  

In December 2024, ECDC hosted the second meeting of the Blood Group from ECDC’s Network for the Microbial 
Safety of Substances of Human Origin (SoHO-Net)2. This meeting included a session dedicated to the risk of 
DENV infection in the EU/EEA. To support discussions during this session, prior to the meeting ECDC 
disseminated a survey to the Blood Group of SoHO-Net on the blood donor assessment and deferral strategies in 
EU/EEA countries related to DENV. This report aims to present the results of this survey. 

Methods 

Between 28 October 2024 and 22 November 2024, ECDC shared an online survey on deferral criteria and testing 
strategies for dengue in blood donors in EU/EEA countries to the national focal points (NFP) of the ECDC SoHO-
Network Blood Group.The survey questions are detailed in the annexes. The survey data were collected and 
managed using REDCap electronic data capture tools hosted at ECDC [26]. Collected data were analysed in 
Excel.  

For the context of this document, dengue-endemic countries are defined as countries with transmission of 
dengue over several seasonal cycles [27]; non-endemic countries are defined as countries with sporadic 
(including seasonal clusters in EU/EEA) or no cases of transmission. Affected areas are defined as areas with 
autochthonous transmission of dengue in the current transmission season [28]. 

Results 

The NFPs from 22 of 30 EU/EEA countries replied to the survey: Austria, Cyprus, Czechia, Denmark, Estonia, 
Finland, France, Germany, Greece, Hungary, Iceland, Italy, Latvia, Malta, The Netherlands, Norway, Portugal, 
Romania, Slovakia, Slovenia, Spain, and Sweden.  

Safety measures 
Among the responding countries, 16 (73%) declared that they had specific deferral criteria for individuals with a 
dengue diagnosis, 20 (91%) had specific deferral criteria for travellers returning from endemic areas (e.g. South 
America), and 12 (55%) had specific deferral criteria for travellers returning from an affected non-endemic area, 
such as EU/EEA countries with autochthonous outbreaks (Table 1).  

1   Recipients DENV RNA negative and IgM negative, or data not available, before transfusion and DENV RNA positive after 
transfusion were classified as probable transmission cases; recipients DENV RNA negative and IgM negative before 
transfusion and DENV RNA negative and IgM positive after transfusion were classified as possible transmission cases. 

2   https://www.ecdc.europa.eu/en/about-ecdc/what-we-do/partners-and-networks/disease-and-laboratory-networks/network-

microbial  

4 

 
 
 
Deferral criteria and testing strategies for dengue virus in blood donors returning from affected areas  

ECDC ASSESSMENT 

Table 1. Presence of deferral criteria related to dengue virus infections for prospective donors with 
a dengue diagnosis, prospective donors returning from endemic areas, and prospective donors 
returning from affected non-endemic areas 

Country 

Austria 

Belgium 

Bulgaria 

Croatia 

Cyprus 

Czechia 

Denmark 

Estonia 

Finland 

France 

Germany 

Greece 

Hungary 

Iceland 

Ireland 

Italy 

Latvia 

Liechenstein 

Lithuania 

Luxembourg 

Malta 

Netherlands 

Norway 

Poland 

Portugal 

Romania 

Slovakia 

Slovenia 

Spain 

Sweden 

NR: not reported. 

Prospective donors 
with a dengue 
diagnosis 

Prospective donors 
returning from 
endemic areas 

Yes 

NR 

NR 

NR 

Yes 

Yes 

Yes 

No 

Yes 

Yes 

No 

Yes 

No 

Yes 

NR 

Yes 

No 

NR 

NR 

NR 

Yes 

Yes 

Yes 

NR 

Yes 

No 

Yes 

Yes 

Yes 

Yes 

Yes 

NR 

NR 

NR 

Yes 

Yes 

Yes 

Yes 

Yes 

Yes 

No 

No 

Yes 

Yes 

NR 

Yes 

Yes 

NR 

NR 

NR 

Yes 

Yes 

Yes 

NR 

Yes 

Yes 

Yes 

Yes 

Yes 

Yes 

Prospective donors 
returning from 
affected non-endemic 
areas 
No 

NR 

NR 

NR 

Yes 

Yes 

No 

No 

Yes 

Yes 

No 

No 

No 

No 

NR 

Yes 

No 

NR 

NR 

NR 

Yes 

Yes 

No 

NR 

Yes 

No 

Yes 

Yes 

Yes 

Yes 

Deferral periods for prospective donors presenting for blood donation with a dengue diagnosis were reported by 
16 countries. This period ranged from 14 days (a non-specific deferral period following an infection) to 180 days 
after clinical resolution, with a median and mode of 120 days. Deferral periods for prospective donors returning 
from endemic areas were provided by 18 countries and were generally 28 days. Similarly, 10 of the 12 countries 
that have specific deferral criteria for travellers returning from an affected non-endemic area indicated deferral 
periods of 28 days (Table 2). 

Deferral criteria and periods are described in national recommendations or guidelines for 19 countries (86%) and 
in regional recommendations for two countries (9%). These criteria may be recommendations or advice, and not 
necessarily formal requirements in some countries. 

The survey included a question asking for estimates of the number of prospective blood donors that had been 
deferred due to a risk of DENV infection in the previous two years. Only one country could provide such 
information: Portugal with a total of 450 donors who deferred during the period 2023−2024.  

5 

 
 
Deferral criteria and testing strategies for dengue virus in blood donors returning from affected areas  

ECDC ASSESSMENT 

Table 2. Duration of deferrals in EU/EEA countries for prospective donors with a dengue diagnosis, 
individuals returning from endemic areas, and individuals returning from affected non-endemic areas 

Prospective donors 
with a dengue 
diagnosis 

Prospective donors 
returning from 
endemic areas 

Prospective donors 
returning from 
affected non-endemic 
areas 

Min – Max 

14–180 days* 

28–30 days* 

Median and mode 

Responding countries 

120 days 

16 

28 days 

18 

28 days 

28 days 

10 

* Deferral periods in months were converted to days, calculated as 30 days for one month, 120 days for four months, and 180 
days for six months.  

Trigger for safety measures  
Twelve countries (55%) use thresholds based on the size of an outbreak to decide on the implementation of 
deferral criteria for donors returning from an affected area. For affected areas in non-endemic countries with 
local outbreaks, this threshold is defined as at least one autochthonous case by five countries and on a case-by-
case basis by six countries. One country considers safety measures for outbreaks of 20 autochthonous cases or 
more, and where ongoing transmission is expected (Table 3).  

Table  3.  Criteria  to  trigger  the  implementation  of  deferrals  for  prospective  donors  returning  from 
affected areas in non-endemic countries  

Country 

Austria 

Belgium 

Bulgaria 

Croatia 

Cyprus 

Czechia 

Denmark 

Estonia 

Finland 

France 

Germany 

Greece 

Hungary 

Iceland 

Ireland 

Italy 

Latvia 

Liechtenstein 

Lithuania 

Luxembourg 

Malta 

Netherlands 

Norway 

Poland 

Portugal 

Romania 

Slovakia 

Slovenia 

Spain 

Sweden 

NR: not reported.  

Criteria 

None defined 

NR 

NR 

NR 

None defined 

None defined 

More than one human autochthonous case 

None defined 

Case-by-case assessment 

One human autochthonous case 

NR 

None defined 

Case-by-case assessment 

Case-by-case assessment 

NR 

One human autochthonous case 

NR 

NR 

NR 

NR 

None defined 

20 human autochthonous cases with ongoing transmission expected  

Case-by-case assessment 

NR 

One human autochthonous case 

None defined 

None defined 

One human autochthonous case 

Case-by-case assessment 

Case-by-case assessment 

6 

 
 
 
 
 
Deferral criteria and testing strategies for dengue virus in blood donors returning from affected areas  

ECDC ASSESSMENT 

Scope of affected areas 
The level of the geographical area considered for the evaluation of dengue risk in the donor assessment varies 
for endemic and non-endemic countries and depending on whether the prospective donor is returning from an 
affected area in an EU/EEA country. For endemic countries outside of the EU/EEA, 16 EU/EEA countries consider 
the geographical level to be the country. For non-endemic countries outside of the EU/EEA, the level of the 
‘affected area’ was most frequently the country (seven countries, 32%), but was also defined at the regional or 
municipal by three countries (14%). For non-endemic countries in the EU/EEA, the level is the country in four 
countries (18%), the administrative region (either NUTS2 or NUTS33) in four countries, the municipality in two 
countries (9%), and based on other definitions in two countries. (Table 4). 

Table 4. Geographical extent of ‘affected areas’ considered for the evaluation of dengue risk in the 
donor assessment in EU/EEA countries by endemicity status  

Country 

Austria 

Belgium 

Bulgaria 

Croatia 

Cyprus 

Czechia 

Denmark 

Estonia 

Finland 

France 

Germany 

Greece 

Hungary 

Iceland 

Ireland 

Italy 

Latvia 

Liechtenstein 

Lithuania 

Luxembourg 

Malta 

Netherlands 

Norway 

Poland 

Portugal 

Romania 

Slovakia 

Slovenia 

Spain 

Sweden 

Endemic countries 

Non-endemic 
countries in EU/EEA 

Non-endemic and 
non-EU/EEA countries 

Country 

NR 

NR 

NR 

Country 

Country 

Administrative region 

Country 

Country 

Country 

NR 

Country 

Administrative region 

Country 

NR 

Administrative region 

NR 

NR 

NR 

NR 

Country 

Country 

Country 

NR 

Country 

Country 

Country 

Country 

Country 

Country 

NR 

NR 

NR 

NR 

Country 

Country 

NR 

NR 

NUTS3 

Affected area 

NR 

NR 

NR 

NR 

NR 

NR 

NR 

NR 

NR 

Country 

Country 

NR 

NR 

Country 

Affected area 

NR 

NR 

NR 

NR 

NR 

Based on information 
published by ECDC  
NR 

Based on information 
published by ECDC 
NR 

NR 

NR 

NR 

Municipality 

NUTS3 

NR 

NR 

NUTS2 
Country if more than two 
regions are affected 
NR 

Country 

Country 

Municipality 

NUTS3 

NR 

NR 

NR 

Municipality 

Country 

NR 

NR 

Country 

NR 

Country 

Country 

Municipality 

Administrative region 

NR: not reported. NUTS: Nomenclature of territorial units for statistics. 

3 https://ec.europa.eu/eurostat/web/nuts  

7 

 
 
 
Deferral criteria and testing strategies for dengue virus in blood donors returning from affected areas  

ECDC ASSESSMENT 

Testing strategies 
Three countries (14%) indicated testing prospective donors at risk of DENV infection as an alternative to 
deferral: Cyprus, France, and Italy. All three countries reported individual donation DENV RNA NAT screening. 
Cyprus and Italy reported testing 2 732 and 4 000 prospective donors respectively in 2024, with no positive 
findings for DENV.  

Pathogen reduction technologies 
Eleven countries (50%) reported the use of pathogen reduction technologies for platelets or plasma, either at 
the national or regional level, regardless of the risk of DENV infection. Of the eleven countries, ten reported the 
use of these technologies for platelets and seven for plasma (Table 5).  

Table 5. Use of pathogen reduction technologies in EU/EEA countries 

Country 

Austria 

Belgium 

Bulgaria 

Croatia 

Cyprus 

Czechia 

Denmark 

Estonia 

Finland 

France 

Germany 

Greece 

Hungary 

Iceland 

Ireland 

Italy 

Latvia 

Liechtenstein 

Lithuania 

Luxembourg 

Malta 

Netherlands 

Norway 

Poland 

Portugal 

Romania 

Slovakia 

Slovenia 

Spain 

Sweden 

NR: not reported. 

Platelets 

Plasma 

Yes 

NR 

NR 

NR 

No 

NR 

No 

No 

No 

Yes 

NR 

NR 

No 

Yes 

NR 

No 

No 

NR 

NR 

NR 

No 

Yes 

Yes 

NR 

Yes 

No 

No 

No 

No 

Yes 

Yes 

NR 

NR 

NR 

No 

Yes 

No 

No 

No 

Yes 

Yes 

Yes 

No 

Yes 

NR 

No 

No 

NR 

NR 

NR 

No 

No 

Yes 

NR 

NR 

No 

No 

Yes 

Yes 

Yes 

8 

 
 
Deferral criteria and testing strategies for dengue virus in blood donors returning from affected areas 

ECDC ASSESSMENT 

Assessment and conclusions 
Summary of donor assessment and deferral strategies in 
EU/EEA countries 
Nearly all responding countries reported having existing criteria to assess and defer prospective donors returning 
from dengue-endemic areas. However, only 55% reported criteria to assess and defer prospective donors 
returning from non-endemic countries with affected areas.  

The definition of the geographical size of an affected area varied across reporting countries, and depending on 
whether it concerned an endemic or a non-endemic country. Affected areas in endemic countries were more 
frequently defined at the country level, while in non-endemic countries they were often set at the municipality 
level. Clusters of dengue in non-endemic areas are highly focal due to the limited flight capacity of the 
mosquitoes carrying DENV. As a result, it is considered very unlikely for someone to be infected by a mosquito 
bite outside of a short radius (e.g. 200−250 meters [29]) around infected individuals.  

The most heterogeneous finding across countries was  the trigger for safety measures in the event of outbreaks 
in the EU/EEA. Some countries implement measures with the first reported autochthonous case, whereas others 
perform case-by-case assessments and may only consider outbreaks with an elevated number of cases or a 
rapidly increasing number of cases. Safety measures aim to mitigate the risk that a traveller returning from an 
affected area and infected by DENV presents for blood donation while being both viraemic and asymptomatic. 
The association between the size of an outbreak and the likelihood of a viraemic prospective donor presenting 
for donation without symptoms is unknown in the EU/EEA. This association has was touched upon during an 
outbreak in Rio de Janeiro [25]. The authors estimated that there was one RNA-positive donation per 800 clinical 
dengue cases in the general population of donor-age. However, this number has been estimated in the context 
of a large outbreak in an endemic area where the relative proportion of asymptomatic and clinical cases of 
dengue is probably different to non-endemic areas, due to higher prevalence of antibodies against one or more 
DENV serotypes in the population. This number may not be applicable to the EU/EEA context where the 
prevalence of DENV-naïve individuals is expected to be higher, likely resulting in a lower proportion of 
asymptomatic cases. In this study, the proportion of reported symptomatic disease was estimated at 37%. 

A related element that may be associated with heterogeneity in the criteria triggering safety measures are limitations 
related to surveillance: possible delays and lack of completeness of reported dengue cases in the EU. In the EU, 
surveillance of DENV infections is now established in affected countries but may not be as effective as for endemic 
diseases, such as West Nile virus infections for which there are consolidated systems and greater awareness.  

Countries that recommend safety measures for prospective donors returning from affected or endemic areas do so 
for prospective donors having had an overnight stay in the affected area. It is worth noting that, while considered a 
diurnal species, the peak activity for Ae. albopictus  and Ae. aegypti  is in the early hours of the morning and late 
hours of the afternoon [30,31], periods which should be covered by overnight stays. 

Once implemented, the most frequent preventive measure reported by countries is the temporary deferral for 
travellers returning from an affected area. The reported deferral periods were very homogeneous, with 28 days 
reported by all ten countries providing data. This deferral period covers more than twice the expected incubation 
period for dengue infection (range: 3−10 days [10]) and is identical to the deferral period considered for West 
Nile virus which may simplify the implementation of deferral periods for areas that are affected by both viruses. 
Only three countries reported the use of NAT for the prospective donors returning from affected areas, all other 
countries only reported the use of a 28-day deferral period.  

The survey questionnaire did not include in-depth questions on the safety measures or supporting evidence. More 
detailed safety measures implemented in some EU/EEA countries are described in publicly-available documents [32]. 

Starting from the 2025 season, ECDC will publish weekly surveillance updates on its website. A report including 
maps will describe the ongoing clusters in the EU/EEA, including localisation at municipality level (local 
administrative unit), when reported by affected countries, and the number of reported cases in the cluster. 
Grouping of cases in clusters will be the responsibility of the reporting countries. A cluster will be reported if at 
least one confirmed case of autochtonous dengue has been identified, but clusters can include probable cases as 
well (see annexes for the case definitions). Clusters will be reported as ‘closed’ 45 days after the last reported 
date of symptom onset [28]. 

In the coming years, as part of its designation as an expert institution for the communicable diseases field in the 
SoHO regulation [33], ECDC intends to publish formal guidelines on preventing the transmission of arboviruses 
through SoHO, including DENV. The scope of ECDC’s work on technical guidelines for the prevention of 
communicable disease transmission through SoHO and expected timelines is published on ECDC’s website4.  

4 https://www.ecdc.europa.eu/en/dengue-fever/surveillance-and-disease-data 

9 

Deferral criteria and testing strategies for dengue virus in blood donors returning from affected areas  

ECDC ASSESSMENT 

Gaps and limitations 
This report has several limitations that should be considered. Only 22 out of 30 EU/EEA countries replied to the 
survey, providing an incomplete overview of the safety measures considered by EU/EEA countries for prospective 
blood donors returning from dengue-affected areas. However, it is noteworthy that countries affected by local 
outbreaks dengue virus replied to the survey. The survey was designed to support expert discussions rather than 
provide comphresenive overview of safety measures, and its brevity did not capture the full extent of safety 
measures implemented by countries. Finally, the ssurvey did not include questions on the rationale or evidence 
supporting the safety measures reported by the countries. As a result, the relative benefit of the different 
measures (e.g., temporary deferral or NAT screening) could not be explored.  

Uncertainty and research gaps on the disease 
• 

The proportion of asymptomatic or undetected DENV infection cases in outbreaks occurring in EU/EEA 
countries is unknown. 
The likelihood of severe DENV infection in recipients of blood transfusion in the EU/EEA is unknown.  

• 

Uncertainty and research gaps on the risk for blood transfusion 
• 

The association between the size of an outbreak and the identification of DENV RNA-positive blood donations, 
in the affected area or among returning travellers, is unknown for outbreaks occurring in EU/EEA countries. 
Consequently, a proportionate trigger based on cluster size – including cost-effectiveness considerations – for 
implementing safety measures for affected areas in EU/EEA countries is unknown.  
The value of DENV RNA NAT screening compared to temporary deferral of donors for returning travellers as a 
preventive measure for outbreaks in the EU/EEA is unknown. 
The reasons that can explain the low number of transfusion-transmitted dengue relative to the very high 
number of DENV infections in endemic countries are uncertain. 

• 

• 

10 

 
 
Deferral criteria and testing strategies for dengue virus in blood donors returning from affected areas  

ECDC ASSESSMENT 

References 

1.  Wilder-Smith A, Ooi EE, Horstick O, Wills B. Dengue. Lancet. 2019 Jan 26;393(10169):350-63. Available at: 

https://www.ncbi.nlm.nih.gov/pubmed/30696575 

2. 

Basurko C, Matheus S, Hilderal H, Everhard S, Restrepo M, Cuadro-Alvarez E, et al. Estimating the Risk of 
Vertical Transmission of Dengue: A Prospective Study. Am J Trop Med Hyg. 2018 Jun;98(6):1826-32. 
Available at: https://www.ncbi.nlm.nih.gov/pubmed/29692297 

3.  Gimenez-Richarte A, Ortiz de Salazar MI, Gimenez-Richarte MP, Collado M, Fernandez PL, Clavijo C, et al. 

Transfusion-transmitted arboviruses: Update and systematic review. PLoS Negl Trop Dis. 2022 
Oct;16(10):e0010843. Available at: https://www.ncbi.nlm.nih.gov/pubmed/36201547 

4. 

Punzel M, Korukluoglu G, Caglayik DY, Menemenlioglu D, Bozdag SC, Tekgunduz E, et al. Dengue virus 
transmission by blood stem cell donor after travel to Sri Lanka; Germany, 2013. Emerg Infect Dis. 2014 
Aug;20(8):1366-9. Available at: https://www.ncbi.nlm.nih.gov/pubmed/25062084 

5.  Gajurel K, Dhakal R, Deresinski S. Arbovirus in Solid Organ Transplants: A Narrative Review of the 

Literature. Viruses. 2024 Nov 15;16(11) Available at: https://www.ncbi.nlm.nih.gov/pubmed/39599892 

6. 

7. 

8. 

Lee C, Jang EJ, Kwon D, Choi H, Park JW, Bae GR. Laboratory-acquired dengue virus infection by 
needlestick injury: a case report, South Korea, 2014. Ann Occup Environ Med. 2016;28:16. Available at: 
https://www.ncbi.nlm.nih.gov/pubmed/27057314 

Lee C, Lee H. Probable female to male sexual transmission of dengue virus infection. Infect Dis (Lond). 
2019 Feb;51(2):150-2. Available at: https://www.ncbi.nlm.nih.gov/pubmed/30318968 

Paz-Bailey G, Adams LE, Deen J, Anderson KB, Katzelnick LC. Dengue. Lancet. 2024 Feb 
17;403(10427):667-82. Available at: https://www.ncbi.nlm.nih.gov/pubmed/38280388 

9.  De Santis O, Bouscaren N, Flahault A. Asymptomatic dengue infection rate: A systematic literature review. 

Heliyon. 2023 Sep;9(9):e20069. Available at: https://www.ncbi.nlm.nih.gov/pubmed/37809992 

10.  Chan M, Johansson MA. The incubation periods of Dengue viruses. PLoS One. 2012;7(11):e50972. Available 

at: https://www.ncbi.nlm.nih.gov/pubmed/23226436 

11.  Chagas GCL, Rangel AR, Noronha LM, Veloso FCS, Kassar SB, Oliveira MJC, et al. Risk factors for mortality 
in patients with dengue: A systematic review and meta-analysis. Trop Med Int Health. 2022 Aug;27(8):656-
68. Available at: https://www.ncbi.nlm.nih.gov/pubmed/35761748 

12.  World Health Organization (WHO). WHO Position Paper on Dengue Vaccines, May 2024. Weekly 

epidemiological record. WHO: Geneva, 2024.  Available at: 
https://iris.who.int/bitstream/handle/10665/376641/WER9918-eng-fre.pdf 

13.  Guzman MG, Halstead SB, Artsob H, Buchy P, Farrar J, Gubler DJ, et al. Dengue: a continuing global threat. 

Nat Rev Microbiol. 2010 Dec;8(12 Suppl):S7-16. Available at: 
https://www.ncbi.nlm.nih.gov/pubmed/21079655 

14.  Katzelnick LC, Gresh L, Halloran ME, Mercado JC, Kuan G, Gordon A, et al. Antibody-dependent 

enhancement of severe dengue disease in humans. Science. 2017 Nov 17;358(6365):929-32. Available at: 
https://www.ncbi.nlm.nih.gov/pubmed/29097492 

15.  Zeng Z, Zhan J, Chen L, Chen H, Cheng S. Global, regional, and national dengue burden from 1990 to 
2017: A systematic analysis based on the global burden of disease study 2017. EClinicalMedicine. 2021 
Feb;32:100712. Available at: https://www.ncbi.nlm.nih.gov/pubmed/33681736 

16.  European Centre for Disease Prevention and Control (ECDC). Communicable Disease Threats Report - Week 

5, 24-31 January 2025. ECDC: Stockholm; 2025. Accessible at: 
https://www.ecdc.europa.eu/en/publications-data/communicable-disease-threats-report-24-31-january-
2025-week-5 

17.  European Centre for Disease Prevention and Control (ECDC). Local transmission of dengue virus in 

mainland EU/EEA, 2010-present. ECDC: Stockholm; 2025. Accessible at: 
https://www.ecdc.europa.eu/en/all-topics-z/dengue/surveillance-and-disease-data/autochthonous-
transmission-dengue-virus-eueea 

18.  Kraemer MUG, Reiner RC Jr Brady OJ, Messina JP, Gilbert M, Pigott DM, et al. Past and future spread of the 

arbovirus vectors Aedes aegypti and Aedes albopictus. Nat Microbiol. 2019 May;4(5):854-63.  

19.  Petersen LR, Busch MP. Transfusion-transmitted arboviruses. Vox Sang. 2010 May;98(4):495-503. Available 

at: https://www.ncbi.nlm.nih.gov/pubmed/19951309 

20.  Sabino EC, Loureiro P, Lopes ME, Capuani L, McClure C, Chowdhury D, et al. Transfusion-Transmitted 
Dengue and Associated Clinical Symptoms During the 2012 Epidemic in Brazil. J Infect Dis. 2016 Mar 
1;213(5):694-702. Available at: https://www.ncbi.nlm.nih.gov/pubmed/26908780 

21.  Almeida FJ, Pacheco JT, Farias CGA, de Matos SF, de Morais CO, Guerra GG, et al. Dengue: a hidden threat 

in blood transfusions amidst Brazil's largest outbreak? Lancet Infect Dis. 2025 Jan;25(1):e10. Available at: 
https://www.ncbi.nlm.nih.gov/pubmed/39622264 

11 

Deferral criteria and testing strategies for dengue virus in blood donors returning from affected areas  

ECDC ASSESSMENT 

22.  Limothai U, Tachaboon S, Dinhuzen J, Singh J, Leewongworasingh A, Watanaboonyongcharoen P, et al. 

Dengue virus transmission risk in blood donation: Evidence from Thailand. J Med Virol. 2024 
Jun;96(6):e29689. Available at: https://www.ncbi.nlm.nih.gov/pubmed/38818789 

23.  Levi JE. Dengue Virus and Blood Transfusion. J Infect Dis. 2016 Mar 1;213(5):689-90. Available at: 

https://www.ncbi.nlm.nih.gov/pubmed/26908779 

24.  Gimenez-Richarte A, de Salazar MO, Arbona C, Gimenez-Richarte MP, Collado M, Fernandez PL, et al. 

Prevalence of Chikungunya, Dengue and Zika viruses in blood donors: a systematic literature review and 
meta-analysis. Blood Transfus. 2022 Jul;20(4):267-80. Available at: 
https://www.ncbi.nlm.nih.gov/pubmed/34694219 

25.  Busch MP, Sabino EC, Brambilla D, Lopes ME, Capuani L, Chowdhury D, et al. Duration of Dengue Viremia 

in Blood Donors and Relationships Between Donor Viremia, Infection Incidence and Clinical Case Reports 
During a Large Epidemic. J Infect Dis. 2016 Jul 1;214(1):49-54. Available at: 
https://www.ncbi.nlm.nih.gov/pubmed/27302934 

26.  Harris PA, Taylor R, Minor BL, Elliott V, Fernandez M, O'Neal L, et al. The REDCap : Building an international 

community of software platform partners. J Biomed Inform. 2019 Jul;95:103208. Available at: 
https://www.ncbi.nlm.nih.gov/pubmed/31078660 

27.  Domanovic D, Giesecke J. How to define an area where transmission of arthropod-borne disease is 

occurring Eurosurveillance. 2012;17(20)  

28.  European Centre for Disease Prevention and Control (ECDC). Public health guidance for assessing and 

mitigating the risk of locally-acquired Aedes-borne viral diseases in the EU/EEA. Stockholm: ECDC; 2025. 
Available at: https://www.ecdc.europa.eu/en/publications-data/public-health-guidance-assessing-and-
mitigating-risk-locally-acquired-aedes-borne 

29.  Haut Conseil de la santé publique (HSCP). Dengue et chikungunya: mesures pour la sécurité 

transfusionnelle et des greffes. HSCP: Paris; 2019. 
https://www.hcsp.fr/explore.cgi/avisrapportsdomaine?clefr=722 

30.  Lima-Camara TN. Activity Patterns of Aedes Aegypti and Aedes Albopictus (Diptera: Culicidae) under 

Natural and Artificial Conditions. Oecologia Australis. 2010;14(03):737-6 

31.  Muhammad NAF, Abu Kassim NF, Ab Majid AH, Abd Rahman A, Dieng H, Avicor SW. Biting rhythm and 
demographic attributes of Aedes albopictus (Skuse) females from different urbanized settings in Penang 
Island, Malaysia under uncontrolled laboratory conditions. PLoS One. 2020;15(11):e0241688. Available at: 
https://www.ncbi.nlm.nih.gov/pubmed/33175896 

32.  European Centre for Disease Prevention and Control (ECDC). Repository of Policy and Practice Resources. 

ECDC: Stockholm; 2025. Available at: https://qap.ecdc.europa.eu/public/extensions/repository-
ppr/repository-ppr.html.   

33.  European Commission (EC). Regulation (EU) 2024/1938 of the European Parliament and of the Council of 
13 June 2024 on standards of quality and safety for substances of human origin intended for human 
application and repealing Directives 2002/98/EC and 2004/23/EC. Available at: https://eur-
lex.europa.eu/legal-content/EN/TXT/?uri=OJ:L_202401938 

34.  European Commission (EC). Commission Implementing Decision (EU) 2018/945 of 22 June 2018 on the 

communicable diseases and related special health issues to be covered by epidemiological surveillance as 
well as relevant case definitions. EC: Brussels, 2018.  at: https://eur-lex.europa.eu/legal-
content/EN/TXT/PDF/?uri=CELEX:32018D0945&from=EN. 

12 

 
 
 
Deferral criteria and testing strategies for dengue virus in blood donors returning from affected areas  

ECDC ASSESSMENT 

Annex 1. Survey 

13 

 
 
 
Deferral criteria and testing strategies for dengue virus in blood donors returning from affected areas  

ECDC ASSESSMENT 

14 

 
 
 
Deferral criteria and testing strategies for dengue virus in blood donors returning from affected areas  

ECDC ASSESSMENT 

Annex 2. Dengue virus infection EU case 
definition[34] 

Clinical criteria 

• 

Fever. 

Laboratory criteria  

A. Probable case 

•  Detection of dengue specific IgM antibodies in a single serum sample. 

B. Confirmed case 

At least one of the following five: 

Isolation of a dengue virus from a clinical specimen; 

• 
•  Detection of dengue viral nucleic acid from a clinical specimen; 
•  Detection of dengue viral antigen from a clinical specimen; 
•  Detection of dengue specific IgM antibodies in a single serum sample AND confirmation by neutralization; 
• 
Seroconversion or four-fold antibody titre increase of dengue specific antibodies in paired serum samples. 

Epidemiological criteria 

History of travel to, or residence in an area with documented on-going transmission of dengue, within the two-
week period prior to the onset of symptoms.  

Case classification 

A. Possible case: not applicable.  

B. Probable case 

Any person meeting the clinical and the epidemiological criteria, and the laboratory criteria for a probable case. 

C. Confirmed case 

Any person meeting the laboratory criteria for a confirmed case. 

15