def extract_disease(risk_assessment):
  """Extracts disease from a RiskAssessment resource.

  Example resource:
  {
    ...
    "basis": [
      {
        "reference": "Patient/610c6252-34de-4493-a3b4-f7ecc43e5681"
      },
      {
        "reference": "QuestionnaireResponse/9c318953-f6b3-492c-aa76-a9564a3cbeba"
      }
    ],
    "prediction": [
      {
        "outcome": {"coding": [{"display": "Measles"}]},
        "qualitativeRisk": {
          "coding": [
            {
              "code": "low",
              "system": "http://hl7.org/fhir/risk-probability"
            }
          ]
        }
      }
    ],
    "resourceType": "RiskAssessment",
    ...
  }

  Design is that there is only one disease and risk probablity per resource, so
  we hardcoded the indexes here and below.
  """
  return risk_assessment['prediction'][0]['outcome']['coding'][0]['display']