More questions on Seas et al. (2000)

I am discussing Seas et al. 2000a in more detail as this is an article that have shown the existence of V. cholerae in Peruvian waters before the outbreak of cholera.

           

As indicated in the previous blog, the existence of toxigenic V. cholerae in Peru was suggested based on the medical records obtained from nine different hospitals in seven cities along the Northern coast of Peru over the five-month period (September–January) during 1989/1990 and 1990/1991. These hospitals were the largest maintained by the Government of Peru in those cities. Out of more than 3000 patients with diarrhea, seven patients from 1990-1991 period were identified as cholera patients based on the clinical signs (i.e. acute watery diarrhea, severe dehydration with shock, generalized cramps, and signs of severe fluid loss, such as ‘‘washerwoman’s hands,’’ sunken eyes, hoarse voice, poor skin turgor, and oliguria). There were no cases reported from 1989-1990 periods. Authors claimed that these 7 cases were indeed cholera infection and was not caused by other infectious or non-infectious agents.

However, the conclusions of the authors derived from these medical records are questionable because

1. A microbiological confirmation of the above 7 cases is lacking. How can it be assumed that the illness was due to V. cholerae itself based on clinical symptoms alone? In fact, other bacterial species that has the potential to cause acute watery diarrhea are prevalent in Peru (Begue et al. 1994). Out of 143 cases of diarrhea surveyed from December 1992 through May 1993 (i.e. after the cholera outbreak), 31% of the cases were caused by Vibrio cholerae whereas enterotoxigeic E. coli was responsible 22% of the cases and Salmonella, Shigella, Campylobacter, and Aeromonas species were responsible for 10% of the cases (Begue et al. 1994). Similarly, a surveillance of bacterial pathogens associated with acute diarrhea in Lima, Peru between January and April 1995 revealed the role of not only V. cholerae but also other enterobacterial species in causing acute diarrhea (Seas et al. 2000b). Many of the clinical symptoms associated with cholera such as watery diarrhea, dehydration, washerwoman’s hand, sunken eyes, hoarse voice were also observed in those bacterial infections (Seas et al. 2000b). In addition, there are many viral and parasitic infections that can cause acute diarrhea and dehydration. Hence the assumption that V. cholerae was responsible for the above 7 cases based on clinical signs alone is not scientifically acceptable.

2. How did the authors rule out other etiologies in the above 7 cases of illness?  

As per the authors, “All of these other etiologies seem unlikely, however, since no similar cases were identified during the same period in the previous year”. This statement is indeed surprising. Why anyone should expect similar cases in the previous year if it were due to other etiologies?

3. The authors have only reviewed the medical records during two year periods i.e. 1989/1990 and 1990/1991. Based on the records from just two years, authors concluded that the above cases could not be due to other infectious or non-infectious agents. Since medical records of just two years can not reveal much regarding the previous presence or absence of an illness, logic seems to be questionable.

4. Lipp et al. 2002 went further ahead to suggest that multiple strains of V. cholerae could have contributed to the epidemic. What is the basis of such assumption?

To me, this article does not reveal or demonstrate anything regarding the previous presence of V. cholerae in Peru. It is highly unfortunate that, based on clinical signs alone, the presence of cholera in Peru before January 1991 was suggested. Without any supporting data, the authors also suggested that climatic factors might have played a role in the outbreak through the activation of V. cholerae that were already present in Peru.

Next-Blame it on to El Nino or La Nina

Seas et al. 2000a. New insights on the emergence of cholera in Latin America during 1991: The Peruvian experience. Am. J. Trop. Med. Hyg. 62(4): 513-517.

Begue et al. 1994. Diarrheal disease in Peru after the introduction of cholera. Am. J. Trop. Med. Hyg. 51(5): 585-589.

Seas et al. 2000b. Surveillance of bacterial pathogens associated with acute diarrhea in Lima, Peru. Int J Infect Dis. 4(2):96-99.

Lipp et al. 2002. Effects of global climate on infectious disease: the cholera model. Clinical Microbiology Reviews 15(4): 757-770.