This report documents a large outbreak of beriberi due to thiamine deficiency among soldiers in Mogadishu exposed to a severely restricted diet. Although thiamine deficiency and beriberi have been common throughout history, large outbreaks of this type have been rare during the last 50 years.
Thiamine, or vitamin B1, is a water-soluble vitamin. The active form, thiamine pyrophosphate, functions as an essential coenzyme in the metabolism of carbohydrates. Body stores of thiamine are limited, and individuals subjected to a thiamine-poor diet can deplete body stores within one to three months 
. The clinical syndrome associated with thiamine deficiency is called beriberi; it is often referred to as wet or dry, depending on whether cardiac or neurologic symptoms predominate. The predominant cardiac symptoms of wet beriberi are more common among young, physically active males 
and are related to impaired carbohydrate metabolism resulting in lactic acidosis, leading to peripheral vasodilatation, high output cardiac failure, and pulmonary and peripheral edema 
. In severe cases, rapid and fulminant cardiac collapse can occur, a rare syndrome called shoshin beriberi 
. Although symptomatic thiamine deficiency occurs regularly in alcoholic patients with poor diets, outbreaks of beriberi are extremely rare and in modern times have been limited primarily to groups subjected to severely restricted diets, such as prison populations 
, detainees 
, and refugees 
The initial appearance of this outbreak presented a diagnostic quandary. Because of the unusual but very consistent characteristics of the presenting cases, a wide range of diagnoses were considered, including toxic ingestion, a variety of infectious diseases, inhalational injury, and several metabolic abnormalities. Based on the epidemiologic evidence, including an ongoing exposure to a monotonous and severely restricted diet, clinical evidence of rapid response to therapeutic thiamine administration, and laboratory evidence of increased erythrocyte transketolase activation coefficient, we believe that thiamine deficiency causing wet beriberi best explained this outbreak. Our case-control study, although limited by a small number of controls, supported the conclusion that the outbreak was related to diet: cases were significantly less likely than controls to have reported supplementing their diet with local foods obtained from the community in the two months prior to the case-control study. Cases were also more likely than controls to report feeling that their lives were constantly under threat, suggesting a risk of illness associated with poor security and likely decreased access to outside (locally-produced) sources of food.
Factors known to increase the risk of thiamine depletion include fever, which can increase metabolism; a diet which relies on polished rice as a primary source of carbohydrates; physical exertion, which raises the bodily requirements of thiamine; and a high ratio of carbohydrates to fat in the diet, which can increase thiamine utilization 
. Thiamine is utilized in the metabolism of carbohydrates; for AMISOM troops, who consume high carbohydrate diets, thiamine requirements are high. Although the diet of the troops was not completely devoid of thiamine, we hypothesize that high thiamine requirements combined with a restricted diet increased the risk of thiamine deficiency and led to sporadic cases of beriberi among these troops. Mass supplementation of the troops with a multivitamin that included thiamine, and diversification of the diet, led to a pronounced decrease in new cases. Although additional cases did occur after our intervention was initiated, no further deaths were reported from this illness, and the outbreak gradually subsided.
The diagnosis of thiamine deficiency is often not straightforward, making the identification and management of thiamine-deficient patients difficult. The severity of thiamine deficiency disease is not always consistent with thiamine levels. During the investigation of an outbreak in a drug rehabilitation facility in Malaysia, testing of a large cohort of both affected and unaffected inmates (n
154) revealed an equal prevalence of thiamine deficiency among symptomatic and asymptomatic inmates 
. Even after supplementation for three weeks in deficient patients, thiamine levels may not normalize in some patients 
. Further confusing the issue, thiamine depletion may be a marker for other micronutrient deficiencies, signaling a population at high risk for other nutritional problems. While multivitamin supplementation may improve the situation initially, dietary diversification is essential to ensure that any co-existing micronutrient deficiencies are corrected.
Our investigation is subject to several limitations. The investigation in Mogadishu was conducted amid extreme security constraints, which limited the access of the investigative team to the site of the outbreak. As a result, detailed dietary information, including the theoretical-thiamine content of a standard food ration, and the quantities of different menu items consumed by cases and controls, were not available for review and dose-response relationships could not be established. Similarly, detailed clinical and demographic information was not readily available for cases presenting before August 20, 2009, possibly limiting the completeness of our data. Data regarding neurological findings for cases in Mogadishu were not systematically collected or available for inclusion in this investigation, limiting out ability to document the range of neurologic involvement. However, for the 33 cases examined and followed in Nairobi, no neurologic deficits were documented. In addition, frequent routine troop rotations in Mogadishu likely affected the natural history of thiamine deficiency in the troops; the exposed population was not a single cohort. Healthy troops were rotated in and troops with months of exposure to the diet in Mogadishu were rotated out. These troop rotations further limited the availability of cases for follow up interviews, and we were not able to determine risk factors for illness among troops who became ill after the supplementation efforts began. Also, although testing on 16 cases showed increased levels of erythrocyte transketolase activation coefficient in all samples, consistent with thiamine deficiency, we did not test all cases, nor did we test controls.
Interestingly, a similar outbreak characterized by lower extremity edema, palpitations and dyspnea occurred among Somali frontier guards of the British East Africa Command in February 1942. Investigation revealed an inadequate diet, including “one orange per week” and a diet devoid of meat for two months. Rapid improvement was noted following therapeutic injection with thiamine, and the etiology of the outbreak was determined to be beriberi. Eighteen cases were identified in total, and the outbreak responded to dietary diversification 
. Although evidence in the 1942 and the 2009–2010 outbreaks points clearly to the consumption of a thiamine-deficient diet, the recurrence of an extremely unusual event among Somalia-based troops warrants the consideration of the additional role, perhaps environmental in nature, of anti-thiamine factors 
. In previous outbreaks, exposures related to the ingestion of thiaminase-containing products (e.g., betel nut, shellfish, poorly-cooked fish, substances high in tannin, and locally grown plants such as ferns) have been implicated in thiamine deficiency and beriberi 
. Additionally, colonization of the intestines by thiaminase bacteria can lower thiamine levels by destroying ingested thiamine despite adequate dietary consumption 
. Among AMISOM troops in Mogadishu, we were not able to elicit a history of exposure to anti-thiamine factors which could explain this outbreak.
Historically, very large outbreaks of beriberi occurred in Japan and have been hypothesized to be due to Citreoviridin, a mycotoxin produced by molds common in rice and which is known to cause a syndrome similar to wet beriberi in experimental animals 
. The affected rice can be discolored (brown or yellow, depending on the mold). Elimination of beriberi in Japan was attributed to improvements in rice quality. Recent investigations of cases of beriberi in Brazil have supported a link to rice, and led to additional calls for improving rice quality 
, but the role of citreoviridin in these cases is disputed 
. In Mogadishu, we did not note any discoloration of the stored rice, although we did not evaluate fungal colonization of rice samples. Once the diagnosis of beriberi was suspected, we did note a general improvement in food quality, which may have led to changes in environmental exposures during the course of this outbreak.
This outbreak of beriberi due to thiamine deficiency occurred in one of the most unstable and insecure settings in the world. The near constant attacks on AMISOM troops have resulted in a relative confinement of troops, and a reduction in the informal supplementation of their diets with locally acquired food items. Although beriberi is a preventable illness, this event must be viewed within the context of the operational and logistical challenges inherent in this environment. This outbreak highlights the need for ongoing nutritional vigilance among groups that are unable to acquire food independently, and that rely entirely on the provision of nutrition by outside sources.