The attachment of murine norovirus 1 (MNV) in biosolids, swine manure, and dairy manure to Romaine lettuce and internalization of this virus were evaluated. The MNV in animal manures had behavior similar to that of pure MNV; however, MNV in biosolids had significantly higher levels of attachment and internalization than pure MNV or MNV in manures. The incubation time did not affect the attachment of MNV in biosolids or manure. Confocal microscopy was used to observe MNV on lettuce after SYBR gold-labeled MNV was added directly to lettuce or after lettuce was submersed in labeled virus. MNV was observed on the lettuce surface, inside open cuts, and occasionally within stomata. In general, lettuce pieces with a long cut on the edge and short cuts on the stem was more likely to contain internalized MNV than intact lettuce pieces, as observed by confocal microscopy; however, while the difference was visible, it was not statistically significant. This study showed that the presence of MNV in biosolids may increase the risk of fresh produce contamination and that the MNV in open cuts and stomata is likely to be protected from sanitization.Noroviruses (NoVs) are leading food-borne pathogens, accounting for over 60% of food-borne disease in the United States (15). They are the most common cause of nonbacterial gastroenteritis, and an estimated 23 million cases occur annually in the United States. NoVs are prevalent in the environment and can be found in waste treatment plant influent and effluent (7), biosolids (4), and animal feces (14). Due to these facts, the use of biosolids and animal manure on agricultural land may disseminate human pathogens in the environment and subsequently increase the chance of crop contamination (22). Recently, increasing outbreaks of NoV infection have been associated with salads and vegetables (9,11,13). Fresh produce could be contaminated from preharvest to postharvest at any point in the chain of production, and one of the major routes with a high likelihood of contamination is the use of contaminated water for irrigation and washing (12). Water could be contaminated by the use of biosolids and manure as organic fertilizer on United States farms or by runoff from animal production zones close to produce fields. Changes in processing, including more cutting and coring performed in the field during harvest, also increase the potential risk of microbial contamination. Furthermore, postharvest sanitizing regimens used by industry have a limited effect on the removal or inactivation of enteric viruses on lettuce (1), and since it only takes a few infectious particles to cause an infection, consumption of fresh produce continues to be a public health risk.Intensive studies of the behavior of bacteria such as Escherichia coli, Pseudomonas, and Salmonella on fresh produce have been conducted (2, 3, 16, 17), but little work has been conducted with viruses. It has been reported that E. coli and Pseudomonas can grow on lettuce surfaces (17). While Pseudomonas tended to adhere to intact leaf surfac...