Epidemiologists tracking the spread of Ebola virus disease are increasingly convinced that the current epidemic in West Africa has been growing exponentially for at least 16 weeks, since May 2014. The number of new cases has been doubling every 20-30 days.

Late last week, epidemiologists at the World Health Organization (WHO) headquarters in Geneva undertook a major re-assessment of all reported data coming from all sources at all outbreak sites.

Though confidence in data being reported by Guinea is good, other significant problems were identified.

In Liberia, for example, data were being reported from four different and uncoordinated streams, resulting in several overlaps and duplicated numbers. In other cases, a backlog of unreported cases was detected, thus creating a distorted picture of how the outbreak has been evolving. Many cases and deaths were not being properly registered on standard reporting forms.

These problems have now been corrected. The results of this data clean-up and re-analysis were published online this week in the New England Journal of Medicine.

Strong control measures to stop steep climb in cases

Nearly 1,000 new cases were reported in the week ending 14 September alone – certainly an underestimate of the true burden of disease. If the present rate of increase continues – if nothing is done to intervene – somewhere between 2,500 and 5,000 cases will occur, each week, just four weeks from now. Affected countries could be seeing more than 10 000 cases weekly by mid-November.

Will the present disaster become a catastrophe?

Not if we implement proven control measures now, says the WHO. Although physical contact with the body fluids of Ebola patients carries a very high risk of infection, the virus does not spread quickly through whole communities.

In this epidemic, each Ebola patient is infecting around two other people, which means that just a two-fold reduction in transmission will be enough to eliminate the virus. In this epidemic, as in previous outbreaks, this should be achievable by early diagnosis, contact tracing, patient isolation, infection control and safe burial.

As the WHO’s assessment shows, these interventions were implemented in Nigeria and Senegal following their first imported cases. Both countries faced many difficult challenges, yet now have achieved good prospects of success.

Looking for signs of hope

There are already signs – though they are not yet convincing – that the number of cases has stopped increasing in some districts in Guinea, Liberia and Sierra Leone, especially those close to the epicentre “hot zone”, where the three countries have common borders, reports the WHO.

If these observations are verified in the coming days or weeks, they will signal the end of exponential growth for Ebola in West Africa, and catastrophe will be averted, according to the WHO.

Worst fears will be replaced by renewed hope that case numbers can be, not only stabilized, but actually forced down by efforts to interrupt transmission. Complete success will put the genie back in the bottle – returning Ebola to its animal reservoir, says the WHO.

With only partial success, Ebola could become a permanent presence in this part of the world. In other words, it could become endemic in the human population, according to the WHO.

A warning for the future

Either way, Ebola 2014 will leave a long legacy: in a rapidly changing world, past experiences with deadly viruses are an imperfect guide to the future. Presumptions are dangerous; vigilance and adaptability are the key.

Scientists and epidemiologists know enough now to issue a clear warning. The risk of future Ebola outbreaks will persist as long as pervasive poverty forces large numbers of people, who depend on bushmeat for their very physical and economic survival, to hunt ever deeper in the region’s degraded and rapidly diminishing forests, according to the WHO.