EXPLORING THE COMBINED ACTION OF LIFETIME ALCOHOL INTAKE AND CHRONIC HEPATOTROPIC VIRUS-INFECTIONS ON THE RISK OF SYMPTOMATIC LIVER-CIRRHOSIS

Although alcohol intake and hepatitis B and C virus (HBV and HCV) infe ctions are the major determinants of liver cirrhosis (LC) in western c ountries, the joint effect of these factors on LC risk has not yet bee n adequately studied. Data from three case-control studies performed i n Italy were used. Cases were 462 cirrhotic patients admitted to Hospi tals for liver decompensation. Controls were 651 inpatients admitted f or acute diseases unrelated to alcohol. Alcohol consumption was expres sed as lifetime daily alcohol intake (LDAI). Three approaches were use d to explore the interaction structure. The Breslow and Storer paramet ric family of relative risk functions showed that an intermediate stru cture of interaction from additive to multiplicative was the most adeq uate one. The Rothman synergism index showed that the interaction stru cture between LDAI and viral status differed significantly from the ad ditive model in particular for high levels of alcohol intake. When mul tiple regression additive and multiplicative models were compared afte r adjustment for the known confounding variables, a trend of the inter action structure towards the multiplicative model was observed at incr easing levels of consumption. Better methods are needed for assessing mixed interaction structures in conditions characterized by multifacto rial etiologies like cirrhosis of the liver.