A slight majority of collapsed runners were normonatremic and spent significantly less time in the medical tent compared with hyper- and hyponatremic athletes. Initial rates of correction of hypernatremia were similar with intravenous and oral hypotonic fluid therapy. Clinicians should be advised that intravenous fluid resuscitation may best benefit hypernatremic collapsed runners who are intolerant to oral fluid ingestion.

A return to normonatremia was not required for hypernatremic runners to "recover" and be discharged from the medical tent. Vomiting either aggravated and/or facilitated the development of hypernatremia. IV administration of 1 L of either (1) a hypotonic solution to hypernatremic runners or (2) an isotonic solution to both normonatremic and hypernatremic runners did not produce any adverse biochemical or cardiovascular changes and can therefore be considered a safe and effective treatment for collapsed runners if used in this context.

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Objectives: To determine the prevalence of self-reported pre-race chronic medical conditions and allergies in ultramarathon race entrants and to explore if these are associated with an increased risk of race-day medical encounters (MEs).Methods: Data from two voluntary open-ended pre-race medical screening questions (Q1history of allergies; Q2 -history of chronic medical conditions/prescription medication use) were collected in 133 641 Comrades Marathon race entrants (2014)(2015)(2016)(2017)(2018)(2019). Race-day ME data collected prospectively over 6 years are reported as incidence (per 1000 starters) and incidence ratios (IR: 95%CI's).Results: Pre-race medical screening questions identified race entrants with a history of chronic medical conditions and/or prescription medication use (6.9%) and allergies (7.4%).The % entrants with risk factors for cardiovascular disease (CVD) was 30% and being older (>45years) and male (27.5%) were the most frequent CVD risk factors. 0.3% of entrants reported existing CVD. The overall incidence of MEs was 20/1000 race starters. MEs were significantly higher in race entrants reporting a "yes" to Q1 (allergies) (IR=1.3; 1.1-1.5) (p=0.014) or Q2 (chronic medical conditions and/or prescription medication use) (IR=1.3; 1.1-1.5) (p=0.0006). Conclusions:Voluntary completion of two open-ended questions identified chronic medical conditions and/or prescription medication use in 6.9% and allergies in 7.4% of ultramarathon race entrants. This is lower than that reported for other races that implemented compulsory completion of a more comprehensive pre-screening questionnaire. Despite potential underreporting, a pre-race self-reported history of chronic medical conditions and allergies was associated with a higher risk of race-day MEs.

Objective: To determine the incidence and nature of illness-related medical encounters (MEs) at a 90-km, ultramarathon, mass, community-based, endurance running event. Design: Retrospective, descriptive epidemiological study. Setting: Comrades Marathon (90 km), South Africa. Participants: One lakh three thousand one hundred thirty-one race starters over 6 years (2014)(2015)(2016)(2017)(2018)(2019). Independent Variables: Incidence of moderate and serious/life-threatening MEs. Main Outcome Measures: All MEs were recorded by race medical doctors on race day each year. Medical encounters were recorded by severity, organ system, and final specific diagnosis (2019 consensus statement definition on mass community-based events). Incidences (I: per 1000 starters; 95% confidence intervals) were calculated for MEs. Results: There were 1971 illness-related MEs, with an overall incidence of 19.1 (range, 18.3-20.0). The incidence for serious/life-threatening MEs was 1.8 (range, 1.6-2.1). Incidences of MEs by organ systems affected were as follows: fluid/electrolyte (8.8; 8.3-9.4), central nervous system (4.0; 3.7-4.5), and gastrointestinal system (2.9; 2.6-3.2). Dehydration (I 5 7.5: 7.0-8.1) and exercise-associated muscle cramping (I 5 3.2: 2.9-3.6) were the 2 most common specific diagnoses. Conclusion: The incidence of MEs in the 90-km Comrades Marathon was one of the highest incidences of MEs reported in an endurance running event (1 in 52 starters and 1 in 556 starters for serious/life-threatening MEs). Preventative measures to reduce MEs are needed, and further investigations into the risk factors associated with MEs could assist in managing the risk and better prepare athletes, race organizers, and medical directors.