2015 Multidrug-resistant Shigellosis Outbreak in the United States

by Véronique CArtier-Archambault and Sandra Daccache

Introduction

Between May 2014 and February 2015 the Center for Disease Control in the United States confirmed 243 cases in 32 states of multidrug-resistant shigellosis. These reported cases can be further broken down to different types of bacteria that cause the disease. Mainly, it was cases of ciprofloxacin-resistant shigellosis picked up by travellers, also known as “Traveller’s Diarrhea/ Montezuma’s Revenge”. However, around 22 cases were of (DAC)shigellosis with decreased susceptibility to azithromycin (a type of antibiotic). Finally, although there were few reports of extremely drug resistant (XDR), this “superbug” strain is the one with the most potential for harm. The rate of reported cases does not seem to be decreasing.

Description of Disease

Shigellosis is an intestinal illness caused by a group of bacteria with the most common being Shigella sonnei. It infects the digestive system causing symptoms ranging from mild to severe diarrhea, bloody stools (dysentery), abdominal pain, and fever. Some humans can be infected for years and not show any signs but still be infecting those around them, thus, aiding in the spread of this highly contagious disease. New strains of the disease being picked up are proving to be resistant to not only to the most commonly prescribed medicines but now resistant to multiple types of antibiotics causing an urgent threat on society because we can longer treat or prevent the disease if someone gets sick. It usually resolves on its own but immuno-compromised people with weaker immune systems and toddlers are now more at risk than ever for developing complications and even death.

Figure 1: A Timeline of the different kinds of multi-drug resistant Shigellosis isolated in the United States. Source: Ciprofloxacin- and Azithromycin-Nonsusceptible Shigellosis in the United States. (2015, June 4). Source: http://emergency.cdc.gov/han/han00379.asp

Figure 1: A Timeline of the different kinds of multi-drug resistant Shigellosis isolated in the United States. Source: Ciprofloxacin- and Azithromycin-Nonsusceptible Shigellosis in the United States. (2015, June 4), http://emergency.cdc.gov/han/han00379.asp

Source of Outbreak

Shigella is commonly acquired when travelling abroad. A study by the CDC on the recent outbreak revealed that half of the 157 cases identified in 32 states were associated with international travel. The countries that the patients had last visited included Dominican Republic (twenty-two cases), Haiti (four), India (eight), Morocco (three), and other destinations in Asia and Europe. The source of this outbreak is impossible to track down to a single place, it rather seems to come from a worldwide increase in ciprofloxacin-resistant Shigella brought back by travelers. In the United States, the consequence of this is a noticeable increase in the resistance of ciprofloxacin among Shigella cases. Abroad, especially in developing countries with poor sanitation, a traveler can easily contract Shigella by eating contaminated food, drinking contaminated water, or by not observing good hand hygiene.

Figure 2:  Shigella sonnei infections suspected resistant to ciprofloxacin among 239 individuals, by isolation date and patient international travel history — United States, May 2014–February 2015. Source: Bowen, A., et al. (2015). Importation and Domestic Transmission of Shigella sonnei Resistant to Ciprofloxacin—United States, May 2014–February 2015. MMWR, 64(12), 318-320.

Figure 2: Shigella sonnei infections suspected resistant to ciprofloxacin among 239 individuals, by isolation date and patient international travel history — United States, May 2014–February 2015. Source: Bowen, A., et al. (2015). Importation and Domestic Transmission of Shigella sonnei Resistant to Ciprofloxacin—United States, May 2014–February 2015. MMWR, 64(12), 318-320.

Cause of Outbreak

After Shigella is imported in the United States by international travelers, it has to be transmitted between individuals to cause an outbreak. The most common transmission mode of Shigella is by fecal-oral contamination. This can happen when an infected person does not maintain a good hand hygiene. Food and water can also be easily contaminated by fecal particles that comes from a diseased individual. It takes a very small dose of this bacteria to cause infection. In fact, only 10 bacterial cells are needed for someone to develop shigellosis. The fact that fecal-oral is a common transmission route and that only a small dose of the bacteria is needed to cause infections are reasons why one or few cases of shigellosis can easily turn into an outbreak.

Certain groups are more at risk concerning the transmission of Shigella. For example, young toddlers, who tend to orally explore their surrounding environment with their tongues and mouth are more at risk of being contaminated. It is estimated that 59% of gastroenteritis in the United States each year is among children under 10 years old. In 2005 there was a large outbreak of multidrug resistant Shigella in Missouri that originated from a daycare center. Again, poor hand hygiene is to blame, especially among toddlers who might not be able to wash themselves properly. In the case of the 2014/15 ciprofloxaxin-resistant Shigella epidemic, the individuals that were the most affected were homeless. Among the 95 cases of ciprofloxacin-resistant Shigella identified in San Francisco, 74 were associated with homelessness or people without a fixed place of residence. The homeless are at high risk of Shigella contamination mainly because of unsanitary conditions as well as poor hygiene and poor diets.

Aftermath

In their official report, the CDC recommended that travelers suffering from diarrhea do not automatically resort to antibiotics, but rather over-the-counter medication that decreases the symptoms of diarrhea, like Immodium. This would reduce the exposure of the bacteria to antibiotics, which would reduce the occurrence of new drug-resistant Shigella. As for the transmission of the disease, no vaccines against Shigella have been developed yet, so good hand hygiene and increased access to hygiene and sanitation infrastructure among vulnerable populations are the key to reduce the intensity of Shigella outbreaks. Also, promising new research is being done on bacteriophage therapy (using “safe/medicinal” viruses that have no harm on the rest of our normal bacteria in our bodies).

Figure 3: An image of Shigellosis inducing bacteria. Source: http://www.cdc.gov/media/releases/2015/p0402-multidrug-resistant-shigellosis.html

Figure 3: An image of Shigellosis inducing bacteria. Source: http://www.cdc.gov/media/releases/2015/p0402-multidrug-resistant-shigellosis.html

References

Arvelo, W., Hinkle, C. J., Nguyen, T. A., Weiser, T., Steinmuller, N., Khan, F., … & Bowen, A. (2009). Transmission risk factors and treatment of pediatric shigellosis during a large daycare center-associated outbreak of multidrug resistant Shigella sonnei: implications for the management of shigellosis outbreaks among children. The Pediatric infectious disease journal, 28(11), 976-980.

Badiaga, S., Raoult, D., & Brouqui, P. (2008). Preventing and controlling emerging and reemerging transmissible diseases in the homeless. Emerging Infectious Diseases, 14(9), 1353.

Bowen, A. (n.d.). Shigellosis. Retrieved November 21, 2015, from http://wwwnc.cdc.gov/travel/yellowbook/2016/infectious-diseases-related-to-travel/shigellosis

Bowen, A., Hurd, J., Hoover, C., Khachadourian, Y., Traphagen, E., Harvey, E., … & Kimura, A. (2015). Importation and Domestic Transmission of Shigella sonnei Resistant to Ciprofloxacin—United States, May 2014–February 2015.MMWR. Morbidity and mortality weekly report, 64(12), 318-320.

Ciprofloxacin- and Azithromycin-Nonsusceptible Shigellosis in the United States. (2015, June 4). Retrieved November 21, 2015, from http://emergency.cdc.gov/han/han00379.asp

Jamal, M., Chaudhry, W. N., Hussain, T., Andleeb, S., Jamal, M., & Das, C. R. (January 01, 2015). Characterization of new Myoviridae bacteriophage WZ1 against multi-drug resistant (MDR) Shigella dysenteriae. Journal of Basic Microbiology.

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