The Hawaii Department of Health has launched a survey seeking to identify all cases of the norovirus that may not have been reported due to a recent outbreak last month.

The survey is directed to all visitors to the Na Pali Coast State Wilderness Park between July 1 to Sept. 4.

The entire Kalalau Trail and campsite will remain closed through Sept. 19 based on DOH’s recommendations, according to the Hawaii Department of Land and Natural Resources.

As of last week, state officials reported at least 37 people reported illnesses after hiking and camping at Kalalau, although the actual number is believed to be higher.

DOH is issuing the survey to help identify norovirus cases that may not have been reported, as well as to gather information from visitors who did not become sick. The information will help officials identify the activities and locations associated with higher risks of illness.

The survey takes less than 10 minutes to complete, health officials said, and responses will remain confidential.

Those who have already reported their illness to DOH are asked to complete the survey, as well.

Norovirus is a very contagious virus that spreads easily on camping trips, especially when clean water supplies are limited, according to the U.S. Centers for Disease Control and Prevention.

People can become infected with norovirus through direct contact with an infected person, by consuming contaminated food or water, or by touching contaminated surfaces and then their mouths.

Symptoms, which usually begin about 24 to 48 hours after exposure, include nausea, vomiting, diarrhea and stomach cramps — and sometimes fever, headache and body aches.

Most people with norovirus illness get better within one to three days, CDC said, but can still spread the virus a few days after. CDC advises people with norovirus not to return to work until at least two full days after symptoms end.

The survey is available at this link.