In 2008, a ten-year-old boy in South Carolina died in his bed an hour after swimming in a pool for the first time. His death was attributed to a phenomenon known as secondary drowning. This condition can be difficult to recognize, since the victim initially appears to be OK after a near-drowning incident. In some cases, however, enough water has entered the lungs to cause a drop in blood oxygen levels, and death may occur between one and 48 hours later. This condition is sometimes confused with dry drowning, in which a laryngospasm causes suffocation.

Inhaling water can leave fluid in the lungs and may cause secondary drowning.

Contrary to popular belief, drowning does not necessarily involve a wholesale ingestion or aspiration of water or other fluids. During cases of secondary drowning, very little fluid is actually present in the victim's lungs. This small amount of liquid is still enough to make the lungs no longer able to deliver life-sustaining oxygen to the bloodstream, however, and the victim eventually succumbs to the lack of oxygenated blood. Death is generally attributed to a pulmonary edema, similar to the effects of acute pneumonia or wet drowning.

Only a small amount of fluid in the lungs can cause secondary drowning.

One thing which makes this condition so difficult to detect is its slow acting nature. A victim may breathe in a very small amount of fluid and believe he or she has successfully expelled it through coughing. In reality, the water may fill up some of the oxygen-rich pores of the lungs, reducing the lungs' ability to oxygenate the blood as it passes through. The heart does not slow down appreciably during this process, so the victim can still walk and talk. The only symptoms may be a sudden change in personality or level of awareness as the blood oxygen level drops over time.

Pulmonary edema refers to a medical condition characterized by the build up of fluid around the lungs.

Victims may or may not feel the effects of secondary drowning immediately. Children and anyone who has experienced a near-drowning should be watched closely after leaving a swimming area. Vomiting or involuntary defecation immediately following a swimming session should be considered a red flag. A sudden change in personality or energy level, such as agitation or extreme lethargy, may be a sign of oxygen deprivation. If a child has inhaled water while swimming, he or she should be observed for several hours for signs of labored breathing or altered mental status. Successful treatment for victims depends on a swift response and a quick diagnosis by trained medical personnel.

Secondary drowning may later strike a patient who appears to be fine after a near-drowning incident.

Often confused with secondary drowning is a condition called dry drowning. Although this condition has a number of causes, it can occur in a near-drowning incident, when the larynx closes to prevent the person from inhaling water or other fluids; this reflex action is known as a laryngospasm. Ordinarily, this laryngospasm should only last 30 to 60 seconds, but in the case of dry drowning, it can continue for several minutes. Meanwhile, the diaphragm drops, creating a partial vacuum in the lungs. Instead of drawing in a breath of outside air, however, this action pulls more oxygen-starved blood into the lungs.