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At this stage there seems to be sufficient agreement among the public health professionals that there is an association between Zika-virus infection during pregancy.on the one hand and 'microcephaly' of the newborn on the other hand. This association is strong, however it does not yet constitiute proof that Zika-virus infection during pregancy causes the microcephaly of the newborn. There may still be other factors that could cause microcephaly that are also linked to the Zika-virus infection (such as potentially the chemicals and toxins that are used to control mosquito populations: in areas of Zika-virus these are used in communities where we observe microcephaly cases).
The association is strong enough to initiate public health actions, one them which will be scientific studies to identify the causal relationship between Zika-virus and microcephaly.
Currently a critical appraisal of the epidemiology of microcephaly (the outcome) in Latin America is missing. In order to have sufficient confidence (more than 95%, for example) about the causal relation between Zikavirus infection during pregnancy (as an exposure) and microcephaly of the newborn (as an outcome), then classic epidemiological studies will be required: studying all determinants of the relationship between exposure and outcome. The determinants may be causal determinants (be it necessary causes or sufficient causes), co-factors or confounders. Such studies will require a close cooperation between Epidemiology (study design and epidemiological analysis) and Microbiology (case definitions, diagnostics, identifying susceptibility).
The European Centre for Disease Prevention and Control (ECDC) in Stockholm, has produced a rapid risk assessment on the potential association between Zikavirus and microcephaly.
This situation underlines the importance fast and adequate scientific studies 'in the field' to assess health risks. Understanding determinants of disease is needed to effectively target the disease through prevention and control measures. This requires a continuous evaluation of scientific evidence of causality.
In ECDC's Rapid Risk Assessment we can recognise the importance public health functions of 'event detection' (surveillance and epidemic intelligence functions present to detect cases), 'treat assessment' (the ability to provide risk assessments, perform outbreak investigations and population based studies) in order to inform those who need to decide on 'threat management'. The availability of competent professional staff in the public health workforce, able to perform these functions is critical for the successful operation of those functions. The key for newly discovered health threats is similar to previously known threats: early detection, early response.