以下文字为某篇科研论文摘要，请分析此摘要的结构组成如背景、目的、方法、结果、结论，需指出每部分结构所包含的文字起始，并根据摘要内容为该论文拟定题目。For decades, the risks of exposure to infectious diseases in recreational beaches has been addressed by measuring abundance of fecal indicator bacteria from water samples through culture methods. Recently, analyses of sand samples for beach quality assessments have been developed as a complement for monitoring recreational waters. In parallel, the growing use of molecular techniques for environmental monitoring has led to obtaining rapid results on the detection of pathogenic genes, providing more accurate information about the health risk of exposure to contaminated sand. The aim of this work was to determine the relationship between the fecal indicator abundance in water and sand. The presence of Shiga toxin-producing Escherichia coli (STEC) by analyzing samples from touristic beaches by culture-dependent (fecal coliforms assay) and culture-independent (real-time PCR of stx1, stx2 and eae genes) methods. We found high CFUs in water and sand along the studied beaches, without an association with sanitation network, nor the level of urbanization. Nevertheless, the highest values (5300 CFU/100mL) was detected in city A. The presence of STEC virulence genes was confirmed in 8 out of 20 sand samples, associated with the lack of sanitation network. The recreational use of sandy beaches may imply a risk to the health of its users, especially near streams and creek outflows, demonstrating the importance of monitoring sand bacteriological quality, and the usefulness of directly monitoring pathogens by means of molecular tools.