Salted Fish and Inhalants as Risk Factors for Nasopharyngeal Carcinoma in Malaysian Chinese1

We conducted a case-control study of nasopharyngeal carci noma among Malaysian Chinese to test inhalants, salted fish consumption, and use of tobacco, alcohol, and nasal ointments as risk factors for the disease. Interviews with 100 cases and 100 controls indicated that salted fish consumption during child hood was a significant risk factor (relative risk, 3.0; p = 0.04); childhood daily consumption of this food item compared to nonconsumption carried a relative risk of 17.4 [95% confidence interval = (2.7,111.1)]. Occupational exposure to smokes (rela tive risk, 6.0; p = 0.006) and to dusts (relative risk, 4.0; p < 0.001) was also significantly associated with nasopharyngeal carcinoma. The two risk factors (consumption of salted fish and exposure to smoke and/or dust) were independent of each other. There was no association between nasopharyngeal carcinoma and tobacco, alcohol, or nasal ointments. For each case interviewed, we sought persons of the same sex who lived in the immediate neighborhood of the patient's residence and who had lived in the study area for the last 5 years. From this group of neighbors we sought as control the person closest in age to the case. All interviews were conducted in the homes of the participants by 2 full-time Chinese interviewers. The interview schedule requested infor mation on use of alcohol, tobacco, and nasal ointments; dietary habits, includingthe consumption of salted fish in childhood and in adolescence; and a complete occupational, residential, and medical history. Standard matched-pair methods (4, 16) were used to analyze the interview data. The data were also analyzed by stratifying on sex and age since, for a number of case-control pairs, close matching in age was not achieved. Results from the stratified analysis were similar to those from the matched analysis. In this report, we present odds ratios and their corresponding significance levels (p values) from the matched analysis. Pairs in which data were missing for either the case or the control were eliminatedfrom analysis.All p valuesquoted are one sided, unless stated otherwise.