Helicobacter-pylori bacteria and duodenal ulcers

Question 1

Recall that the guidelines for judging whether an observed association is a causal relationship are: For each of the following findings regarding Helicobacter-pylori bacteria and duodenal ulcers (DU) specify which of the above guidelines pertains.

Question 2

Please match the causal relationship in the following 3 theoretical examples. (3 points; 1 point each)

a) Necessary and sufficient

b) Necessary but not sufficient

c) Sufficient but not necessary

d) Neither necessary nor sufficient Requirements: answer the questions Temporality Strength Dose-Response / Biological Gradient Consistency Biological plausibility Analogy Experiment Coherence Specificity of the association Helicobacter pylori can infect the mucosa of the intestines causing inflammation bleeding and ulceration.

The investigators used a cohort study design where you follow the same people over time. They enrolled in their study those with H. pylori but with no DU and then followed them up 10 years later to measure the incidence of DU. The most severe cases of DU were associated with the highest levels of H. pylori bacteria and the mildest DU cases had the lowest H. pylori levels. Long-term use of aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs) can disrupt normal enzyme production and function which can lead to ulcers so heavy aspirin/NSAID users were excluded from H. pylori studies yet it was still found that H. pylori infection was associated with DU. Many studies conducted throughout the world have shown that H. pylori is associated with DU. No well-designed study has shown evidence to the contrary. When H. pylori was treated with antibiotics the duodenal ulcers healed. Having high levels of H. pylori is associated with a 4-to-16-fold higher odds of DU compared to those without this bacteria. In addition to duodenal ulcer H. pylori is also found to be associated with stomach cancer and gastric ulcers thus this criterion of causation is not fully met. In the absence of vaccination or early treatment infection by rabies virus always leads to a highly fatal case of rabies. No other virus leads to rabies. ___________ Age is a risk factor for many chronic diseases although some older people never develop chronic diseases and some chronic diseases develop in young people. ___________ Miners who worked in an asbestos factory for a period of 10 or more years always developed lung cancer. Smoking is another cause of lung cancer. ___________ Temporality Strength Dose-Response / Biological Gradient Consistency Biological plausibility Analogy Experiment Coherence Specificity of the association Helicobacter pylori can infect the mucosa of the intestines causing inflammation bleeding and ulceration. The investigators used a cohort study design where you follow the same people over time. They enrolled in their study those with H. pylori but with no DU and then followed them up 10 years later to measure the incidence of DU. The most severe cases of DU were associated with the highest levels of H. pylori bacteria and the mildest DU cases had the lowest H. pylori levels. Long-term use of aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs) can disrupt normal enzyme production and function which can lead to ulcers so heavy aspirin/NSAID users were excluded from H. pylori studies yet it was still found that H. pylori infection was associated with DU. Many studies conducted throughout the world have shown that H. pylori is associated with DU. No well-designed study has shown evidence to the contrary. When H. pylori was treated with antibiotics the duodenal ulcers healed. Having high levels of H. pylori is associated with a 4-to-16-fold higher odds of DU compared to those without this bacteria. In addition to duodenal ulcer H. pylori is also found to be associated with stomach cancer and gastric ulcers thus this criterion of causation is not fully met. In the absence of vaccination or early treatment infection by rabies virus always leads to a highly fatal case of rabies. No other virus leads to rabies. ___________ Age is a risk factor for many chronic diseases although some older people never develop chronic diseases and some chronic diseases develop in young people. ___________ Miners who worked in an asbestos factory for a period of 10 or more years always developed lung cancer. Smoking is another cause of lung cancer. ___________