Under the Deep Blue Sea

Updates from the 10th Conference of the International Society of Travel Medicine

Special Report

By Mary-Louise Scully, MD

Sansum-Santa Barbara Medical Foundation Clinic, Santa Barbara, CA.

Dr. Scully reports no financial relationship relevant to this field of study.

At the recent 10th Conference of the International Society of Travel Medicine (CISTM10) in Vancouver, Canada in May an informative overview of diving medicine was given by Michael Callahan MD as part of a Plenary Session Medicine at the Extremes (PLO1).1 Since scuba diving first began in the mid 1940s, it has grown to now include more than 9 million certified divers in the United States alone. With recent advancements in scuba equipment and its growing popularity, more adventure-minded persons of all ages and degrees of physical fitness are participating in scuba diving. This expansion of participation carries with it increased risk of diving-related injury or illness, especially in persons with underlying medical conditions or disabilities. As such, physicians need to be knowledgeable about assessing their patients' medical fitness for diving.

A diving examination should include an assessment of patients pulmonary, otolaryngologic, cardiac, neurologic systems, as well as their psychological stability. Medical contraindications for diving are often related to the pressure changes that occur with submersion underwater. Some absolute contraindications include pregnancy, a history of spontaneous pneumothorax, atrial septal defectf, and chronic or restrictive lung disease. A complete listing of contraindications is provided in Table 1.2 Some relative contraindications generally include age less than 12 years, significant visual impairment, and arteriovenous malformations (AVMs). Insulin-dependent diabetes mellitus (IDDM) was previously considered a contraindication for diving but many patients with well-controlled IDDM have been diving safely for years and the American Diabetes Association has guidelines for divers with IDDM. Therefore, well-controlled IDDM patients that are knowledgeable, used to vigorous exercise, and who have a prepared diving companion can sometimes be medically cleared for diving. Patients with well-controlled asthma or hypertension can also generally be given medical clearance to dive.

Even with adequate screening, diving complications can occur, the most serious being the pulmonary overpressurization syndrome and decompression sickness . In 1980, the Divers Alert Network, a private, nonprofit dive safety organization was established to provide emergency medical assistance to recreational divers. It is now a worldwide organization with a broad range of activities (www.DiversAlertNetwork.org). Some practical advice for recreational divers is to be sure that there is supplemental oxygen available on the dive boat and to check the status and accessibility of the nearest decompression chamber prior to any diving excursion.

Paul Auerbach, MD, both entertained and educated his audience in an excellent presentation entitled "Shark Attack" as part of the symposium When Nature Bites Back (SY04).3 Sharks are indeed man's most feared underwater creatures. Some 35 of about 375 species of sharks account for the 75 to 100 shark attacks that are estimated to occur annually. There are between 6-10 deaths from shark attacks each year. The most common types of sharks accounting for attacks are the great white sharks, bull sharks, and tiger sharks. However, smaller sharks such as blacktip and spinner sharks are involved in the minor incidents common in the offshore areas of Florida. The greatest numbers of shack attacks are reported from North America, especially Florida's central east coast, and the danger of shark attack is greatest during the summer months.

Sharks are extreme predators that possess remarkable sensory systems, including olfactory and vibratory systems that allow them to track prey up to ½ mile away by motion. Sharks eyes are specially adapted for night vision as well. The possible attraction of sharks to certain colors such as international orange has caused some shark researchers to refer to this color as "yum yum yellow." The concept that sharks appear to be more attracted to bright colors in preference to black seems to be accepted, yet unproven. It is clear that sharks are attracted to bright, reflective type objects so avoidance of jewelry such as ankle bracelets or barrettes is strongly suggested.

There are 2 basic patterns of shark feeding: (1) normal or subdued, with slow purposeful group movements, and (2) frenzied or mob feeding as a result of an inciting event such as the presentation of food or blood in the water. Blood and other body fluids can attract sharks and woman have historically been advised to avoid diving during menstruation, although there is little actual data to support the attraction of sharks to menstrual discharge. Certain sharks will bump a person prior to attack. This so-called "bump and bite" technique is perhaps a shark's way of assessing the defensive abilities of its prey. Severe bruising and abrasions have occurred secondary to even such bumping incidents. If a shark does bump a person, one should prepare for a likely attack.

Sharks commonly attack young, old, or sick prey. It is thought that humans splashing at or near the water's surface are misinterpreted by sharks as struggling prey. Some other important advice about preventing shark attacks include : (1) avoid known shark-inhabited water, particularly at dusk and at night, (2) swim in groups, (3) avoid turbid water, drop-offs, deep channels, mouths of rivers, and sanitation waste outlets, (4) do not carry dead or tethered fish as fish blood is a strong chemical attractant for sharks, (5) do not tease or corner a shark, and (6) do not splash on the surface or behave in a manner that could mimic that of a struggling fish. Lastly, if approached by a shark in shallow water, swimmers should leave the water if possible, facing the shark, with slow purposeful movements. If a shark approaches in deep water, a diver should stay submerged and descend to the ocean floor seeking shelter with posterior protection so as to better defend against a frontal attack. Blunt blows, ideally with a knife or a weapon, aimed at the eyes, snout, or gills are a victim's best tactic to defend against a definite attack. "Bang sticks" and electronic shark deterrent devices are in use and evolving but, unfortunately, they are not fully protective. A powerhead, bang stick, or shark stick is actually specialized type of a firearm for underwater use and firing in direct contact with the target.


  1. Callahan M. Diving Medicine: Pre-travel Screening, Education and Itinerary-based Assessment for Recreational Divers. (PL01.02). 10th Conference of the International Society of Travel Medicine. Vancouver, Canada. May 20-24, 2007.
  2. Kizer K, Van Hoesen K. Diving Medicine. In: Wilderness Medicine. Auerbach PS. (ed) Fifth Edition. 2007, Mosby - Elsevier, Amsterdam, Netherlands.
  3. Auerbach P. Shark Attack. (SY04.01). 10th Conference of the International Society of Travel Medicine. Vancouver, Canada. May 20-24, 2007.