Modeling the Impact

There has been some modelling work done to estimate the potential impact of a pandemic, using data from the 1957 and 1968 pandemics in a model developed by CDC-USA (FluAid - available at http://www2.cdc.gov/od/fluaid/default.htm), but adapted with New Zealand data. This modelling suggested that there would be about 300,000 to 800,000 additional medical consultations required in the first wave of a pandemic lasting about 8 weeks.

Ref: Wilson N, Mansoor O, Baker M. Estimating the impact of the next influenza pandemic on population health and health sector capacity in New Zealand. NZ Med J 2004; 118:U1346. http://www.nzma.org.nz/journal/118-1211/1346/

Of these, 7,000 to 16,000 would require hospitalization and there would be 1600 to 3700 deaths. (NB clearly if these numbers occur NZ hospitals would not manage this amount and different strategies involving managing more sick people in the community would become paramount.) Note that if the virulence of the new virus was like that of the 1918 pandemic, there could be 10 times as many deaths.

Impact in a General Practice:

In looking at the impact on the general practitioner (and using the same model), it was estimated that at its peak there would be a 10% loss of general practitioner days available for work as a result of sickness (or caring for family) from influenza.

Ref: Wilson N, Baker M, Crampton P, Mansoor O. The potential impact of the next influenza pandemic on a national primary care medical workforce. Human Resources for Health 2005, 3:7 http://www.human-resources-health.com/content/3/1/7

This average of 10% is likely to be variably distributed and it is likely that in some practices and areas, that most health providers may be unable to provide care for some time.

It is also predicted by this model that there would be an estimated 83 influenza consultations per GP during the peak week; but if only 50 - 75% of GPs were working during this week (due to illness, or caring for relatives), then the average weekly caseload would rise to 125 - 166 people.

The authors note that "this outcome would make it the worst internal demographic event for New Zealand since the 1918 pandemic". And this is assuming a much lower mortality rate than is now being used for planning purposes by the Ministry of Health.

The above modelling results used incidence rates in the 15% to 35%. The NZ Ministry of Health is currently using 40% incidence as the upper range for its scenarios, and is now using a 2% case-fatality rate that is closer to that of 1918 in contrast than that used in the above model.