August 2014

What Exactly Constitutes a Public Health Emergency of International Concern?

Fri, 29 August 14 10:00

ON 8 AUGUST, the Director-General of the World Health Organisation, Dr Margaret Chan, declared the current outbreak of Ebola virus in West Africa a Public Health Emergency of International Concern (PHEIC), on the basis that the outbreak constitutes an ‘extraordinary event’ and a health risk to bordering states, with the potential for serious adverse consequences if the virus were to spread internationally from its current West African location.

As of 26 August, 3,062 people have become infected and 1,552 people have died of the virus, constituting the largest outbreak since it was discovered in 1976. Even at that, the WHO acknowledges that the death toll may be underestimated. 

The PHEIC declaration is not unreasonable. However, the fact that it is necessary at all raises some important questions for the so-called ‘developed’ world. Why has the current outbreak proven so difficult to contain? What are the chances of the virus spreading to more countries? And when this outbreak is finally over, what can be done to prevent it happening again?

The word outbreak is synonymous with epidemic, and in simple terms indicates more cases of a disease than expected in a given area, or in a specific group of people over a particular period of time. In contrast to the current situation in West Africa, in many situations the causative agent of an outbreak is not known when the first cases of the illness occur, as with severe acute respiratory syndrome (Sars) in 2003. For this reason, infectious disease surveillance programmes are vital to the early detection of emerging or novel infections.

In Ireland, the Health Protection Surveillance Centre (HPSC) coordinates these programmes, liaising at international level with agencies like the European Centre for Disease Prevention and Control (ECDC) and the WHO, that provide regional and global oversight.

The importance of infectious disease surveillance cannot be overstated. In June 1981 for example, the Morbidity & Mortality Weekly Report, published by the Centers for Disease Control in America, described five cases of pneumonia in young homosexual men caused by an organism, Pneumocystis jirovecii (formerly carinii), typically seen in individuals with compromised immune systems. Those individuals turned out to be the first reported cases of HIV infection.

Similarly in 2003 and 2012 respectively, Severe Acute Respiratory Syndrome (Sars), and Middle East Respiratory Syndrome, were identified. Indeed, the first report of Sars – at that time unnamed – appeared on ProMED-Mail, (Program for Monitoring Emerging Diseases) an extant early-warning system established by the International Society for Infectious Diseases in 1994.

When an outbreak is detected and the extent determined, there are two main priorities:

  1. To treat the infected individuals and the people with whom they may already have been in contact; and,
  2. To prevent onward transmission of the infecting agent.

Broadly speaking, infected individuals and their contacts can be treated (or given prophylaxis) with antibiotics or antiviral agent, if treatments exist. For pathogens for which there is no specific therapy, a vaccine may be available: whilst vaccines are predominantly used to protect those individuals who have not yet been exposed to the infection, in certain circumstances they can also be beneficial post-exposure. There is no specific antiviral therapy or vaccine for Ebola virus.

The prevention of onward transmission or spread of the outbreak is the priority for protecting population health, and each outbreak presents its own particular challenges. With Ebola for example, patients are only infectious when they have symptoms, but on account of the virus’ incubation period (ie the time between acquiring infection and developing symptoms), it can take up to 21 days for symptoms to appear.

Therefore, to prevent onward transmission of Ebola, all those who have been exposed to an infected patient should be monitored – ideally in isolation, and protected from additional exposures – for a period of 21 days. People who develop illness in this period should be transferred to a treatment facility, and those who remain well 21 days after their last contact can be safely discharged. One of the challenges in the current outbreak however has been identifying all of those individuals who have been exposed to Ebola-infected patients, some of whom may not realise that they have been exposed or infected.

In contrast to Ebola, individuals infected with measles virus, for example, become infectious about four days before the classic measles rash develops, and the typical incubation period is 10-14 days. Measles is also a highly infectious virus, with a basic reproductive number (R0) of 12-18. (The R0 indicates the average number of people to whom an infected individual is likely to transmit the virus: the equivalent number for Ebola is 1-4.)

Therefore, while measles is usually a less dramatic illness than Ebola, the infection control strategy is more complex, because the virus is more infectious, more readily transmissible (by respiratory droplets or aerosol), and infected individuals are infectious before symptoms appear. It should also be noted that for the majority of the developing world, measles is a far more significant issue than Ebola, with 122,000 deaths globally in 2012 alone.

Knowledge of the pathogen therefore, its natural life cycle, its route of transmission, its incubation period, and its symptomatology all inform outbreak prevention. Dissemination of information in real-time to the international community is also essential. However, it is difficult to prevent the unanticipated. The countries in West Africa have not suffered Ebola outbreaks previously, and therefore lacked the experience and infrastructure necessary to rapidly respond to and contain the disease, besides which the presence of a natural reservoir (fruit bats) for Ebola makes its eradication from all at-risk areas impossible. In contrast, eradication (through vaccination) of polio or measles is possible, and a stated commitment of the WHO.

It is important to realise, though, that outbreak prevention also comprises ‘simpler’ elements, such as clean water, proper sanitation, adequate medical supplies, immunisation programmes, isolation facilities, human resources, mosquito nets, and perhaps most importantly, preparedness planning. Unfortunately however, the majority of severe outbreaks seem to occur in countries and regions that are worst equipped to handle them. This is in part due to certain populations always being at greater risk because of their proximity to wildlife (natural reservoirs), their particular hunting practices, their dietary habits, or their social customs and beliefs.

Ultimately, though, it’s probably because they lack the necessary infrastructure and support, and once the current outbreak is resolved, the eyes (and the wallets) of the world move quickly on to the next humanitarian crisis – and the next new outbreak.

Dr Cillian De Gascun is Consultant Virologist and Laboratory Director at the National Virus Reference Laboratory, UCD. Article first published on 29th August 2014.