21 days quarantine period for Ebola patients is not long enough as deadly virus could still remain in the body- Scientists

The recommended 21-day quarantine period for the Ebola virus is not long enough to contain the spread of the disease, a new study has warned.

The World Health Organisation (WHO) advises the incubation period for the virus is between two and 21 days. 

It is thought that if someone who has been in contact with an Ebola victim but does not develop symptoms after that point, has not been infected.

But a study by scientists at Drexel University in Philadelphia has found there is a 12 per cent chance the deadly virus could lay dormant in a person's body for longer than the three-week period.

It means a significant proportion of the population in West Africa could be developing the disease outside of the key incubation period.

Biologist professor Charles Hass said when calculating the isolation period on the basis of past outbreaks, there is always a 'standard deviation for results' - a percentage by which they may vary - which has yet to be taken into account during this outbreak. 

Professor Hass, who has vast experience of analysing the risk of transmitting biological pathogens, said 'reconsideration is in order' as 21 days may not be sufficient to protect public health.  

He said: 'Twenty one days has been regarded as the appropriate quarantine period for holding individuals potentially exposed to Ebola Virus to reduce risk of contagion, but there does not appear to be a systemic discussion of the basis for this period.'

Data gathered by the WHO from earlier outbreaks in Zaire and Uganda reported an incubation period of between two and 21 days for the virus, meaning if the individual has not presented with symptoms after three weeks they are unlikely to be infected or contagious.

Professor Haas said he believes a broader look at risk factors should be considered as with any research of this nature there is a standard deviation in results.

In the case of Ebola's incubation period the range of results generated from Zaire and Uganda varied little, and this may have contributed to the WHO's certainty.

But looking more broadly at data from other Ebola outbreaks in Congo in 1995 and West Africa recently suggests there could be up to a 12 per cent chance that someone could be infected even after the 21-day quarantine.

Professor Haas, whose research is published in PLOS Currents, said: 'While the 21-day quarantine value, currently used, may have arisen from reasonable interpretation of early outbreak data, this work suggests reconsideration is in order and 21 days might not be sufficiently protective of public health.'

He said these quarantine periods must be determined by looking at the cost of enforcing the quarantine against the that of releasing exposed individuals.

Looking at the potential trade off between costs and benefits as the quarantine time is extended should guide public health officials in determining the appropriate action.

But, with more contagious and potentially deadly diseases the cost of making a mistake on the short side when determining a quarantine is extremely high.

Professor Haas, added: 'Clearly for pathogens that have a high degree of transmissibility and a high degree of severity, the quarantine time should be greater than for agents with lower transmissibility and severity.

'The purpose of this paper is not to estimate where the balancing point should be, but to suggest a method for determining the balancing point.'