Table 1

Risk assessment for trace back of patients with a Viral Haemorrhagic Fever (Lassa fever, Marburg, or Ebola haemorrhagic fever), who travelled on an airplane
Lassa Ebola Marburg
Index case Probable or laboratory confirmed cases can be considered for trace back
A patient could be considered as a probable case of Lassa A patient could be considered as a probable case of Ebola A patient could be considered as a probable case of Marburg
1. Who has symptoms compatible with Lassa (malaise, fever, headache, sore throat, cough, nausea, vomiting, diarrhoea, myalgia, chest pain, hearing loss [33]) AND 1. Who has symptoms compatible with Ebola (sudden onset of fever, intense weakness, muscle pain, headache, sore throat, vomiting, diarrhoea, rash, impaired kidney and liver function, internal and external bleeding [34] AND 1. Who has symptoms compatible with Marburg (abrupt onset, severe headache, severe malaise, muscle aches and pains, high fever, severe watery diarrhoea, abdominal pain and cramping, nausea, vomiting [24]) AND
2. Who had within 21 days of symptom onset 2. Who had within 21 days of symptom onset 2. Who had within 21 days of symptom onset
a) Risk exposure to rats or their droppings in rural areas in West Africa [35] OR a) Risk exposure in Sub-Saharan Africa (medical treatment, contact to body fluids of ill persons, contact with primates or bats in areas with suspected or known Ebola activity [36]) OR a) Risk exposure in Sub-Saharan Africa (medical treatment, contact with body fluids of ill persons, contact with primates or bats. in areas with suspected or known Marburg activity [36]) OR
b) Contact to a case of Lassa (e.g. health care worker, care giver, etc.) b) Contact with a case of Ebola. b) Contact with a case of Marburg.
WHO recommends a case definition for surveillance standards that could be also helpful for contact tracing [37].
Epidemic situation Travel to West Africa Travel to Sub-Saharan Africa
Certain West African countries are considered endemic areas for transmission of Lassa fever [35]. However, non-endemic countries may also be taken into consideration if the passenger has particular risk exposures. Although the epidemiology remains to be determined, a new Arenavirus called Lujo, which is similar to Lassa virus, has been identified in case from Zambia with secondary transmission in South Africa [38]. Certain Sub-Saharan African countries are considered as risk areas for transmission [36]. However not only those African countries where already cases have been reported should be taken into consideration, as the index patient could be the first case to indicate infection in a country. Certain Sub-Saharan African countries are considered as risk areas for transmission [36]. However not only those African countries where already cases have been reported should be taken into consideration, as the index patient could be the first case to indicate infection in a country.
Risk exposure: The reservoir of Lassa virus is a rodent host M.natalensis, in which it is persistent and mostly silent. [39] Outbreaks have also been reported in hospital settings [40]. Risk exposure: Evidence indicates to bats as one of the reservoir of Ebola [41]. On the African continent, Ebola infections of human cases have been linked to direct contact with gorillas, chimpanzees, monkeys, forest antelope and porcupines found dead in the rainforest. [34,42,43]. Human-to-Human transmission has taken place during medical treatment, through direct contact with body fluids of ill or dead persons. Outbreaks have also been reported in hospital settings. This should be taken into consideration when assessing the risk exposure of a probable case. Risk exposure: Evidence indicates to bats as one of the reservoir of Marburg [44,45]. Human-to-Human transmission route is through direct contact with blood or other infected body fluids. Outbreaks have also been reported in hospital settings. This should be taken into consideration when assessing the risk exposure to a probable case.
Effective Exposure Direct contact to body fluids Direct contact with case even if exposure to body fluids was not reported
Contact tracing of a Lassa case, should only be considered if direct contact to body fluids such as blood, urine, faeces or vomit had taken place during the flight. Unless such an incident took place, the likelihood of a transmission is considered negligible. Human-to-human transmission of Ebola virus occurs through direct contact with infectious body fluids. However, Ebola virus has also been detected in sweat [46], and although the risk is very low, passengers who may have had direct contact with the case should be contacted and followed-up, even if exposure to body fluids was not reported. Human-to-human transmission of Marburg virus occurs through direct contact with infected body fluids. As the transmission of Marburg virus through sweat cannot be excluded, and although the risk is very low, passengers who may have had direct contact with the case should be contacted and followed-up, even if exposure to body fluids was not reported.
Timing of flight Detection of the event within 21 days after the flight
The incubation period of Lassa is usually seven to 12 days but may range between three and 21 days [32,47-49]. In order to find potential cases, tracing passengers should only be considered if the flight took place within the previous 21 days. The incubation period of Ebola usually ranges between two and 21 days [50]. Thus in order to find potential cases, tracing passengers should only be considered if the flight happened within the previous 21 days. Incubation period for Marburg ranges between 2 and 14 days [51]. In order to find potential cases within the possible longest incubation period, tracing passengers should only be considered, if the flight happened within the previous 21 days. To have a common approach with the other VHF it was decided to use for Marburg also the 21 days period.
After this time period a message to raise awareness among doctors and public health professionals should be considered. After this time period, a message to raise awareness among doctors and public health professionals could be considered. After this time period a message to raise awareness among doctors and public health professionals could be considered.

Gilsdorf et al.

Gilsdorf et al. BMC Public Health 2012 12:1014   doi:10.1186/1471-2458-12-1014

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