A changing picture of shigellosis in southern Vietnam: shifting species dominance, antimicrobial susceptibility and clinical presentation

Abstract

Background: Shigellosis remains considerable public health problem in some developing countries. The nature of Shigellae suggests that they are highly adaptable when placed under selective pressure in a human population. This is demonstrated by variation and fluctuations in serotypes and antimicrobial resistance profile of organisms circulating in differing setting in endemic locations. Antimicrobial resistance in the genus Shigella is a constant threat, with reports of organisms in Asia being resistant to multiple antimicrobials and new generation therapies.

Methods: Here we compare microbiological, clinical and epidemiological data from patients with shigellosis over three different periods in southern Vietnam spanning 14 years.

Results: Our data demonstrates a shift in dominant infecting species (S. flexneri to S. sonnei) and resistance profile of the organisms circulating in southern Vietnam. We find that there was no significant variation in the syndromes associated with either S. sonnei or S. flexneri, yet the clinical features of the disease are more severe in later observations.

Conclusions: Our findings show a change in clinical presentation of shigellosis in this setting, as the disease may be now more pronounced, this is concurrent with a change in antimicrobial resistance profile. These data highlight the socio-economic development of southern Vietnam and should guide future vaccine development and deployment strategies.

Trial registration: Current Controlled Trials ISRCTN55945881.

Figure 1

The distribution of the residences of cases of childhood shigellosis admitted to the hospital for tropical diseases in Ho Chi Minh City. Over the three periods we were able to positively identify infecting Shigella serotypes in the stools of 297 children with symptoms consistent with shigellosis. Of these patients, 228 (76.8%) children lived in the 23 districts that constitute Ho Chi Minh City. This figure represents the distribution of the homes of patients reporting to the hospital for tropical diseases with Shigella isolated from stool, by district. The percentage of cases reporting from each ward is distinguished by gradual shading. The location of the hospital for tropical diseases is shown by a yellow star. Large waterways (rivers and canals) are shown in dark grey shading.

Figure 2

The combined sex and age distribution of childhood shigellosis patients in southern Vietnam. Graph depicts the combined age and sex distribution (female - red, male - grey) of 297 children with shigellosis. The black line with boxes represents the total number of cases per age group specified. The overall age range was from 3 months to 154 months, with a median of 24 months. There was no significant relationship of shigellosis with gender; in total, 152 patients were male (51.2%) and 145 were female (48.8%).

Figure 3

The seasonal distribution of shigellosis in southern Vietnam. southern Vietnam has two distinct seasons, wet and dry. The combined data were averaged by calculating the number of months represented to get an overall number of cases per month. Red bars; total number of cases, grey bars; average monthly temperature and black line with boxes; average monthly rainfall. The seasonal data represents the average rainfall and temperature per month for Ho Chi Minh City.

Figure 4

The distribution of Shigella species from three childhood shigellosis studies in southern Vietnam over fourteen years. The distribution of Shigella species from period A (n = 80), period B (n = 114) and period C (n = 103). The percentage of S. sonnei and S. flexneri are colored red and grey respectively, other Shigella species are colored black. The p value was calculated using the chi - squared test.

Figure 5

Changing antimicrobial resistance patterns of Shigella spp. All organisms were tested for susceptibility to seven antimicrobial agents by the disc diffusion and E-test methods. The antimicrobials tested were as follows, AMP; Ampicillin, CHL; Chloramphenicol, SXT; Trimethoprim- Sulfamethoxazole, TET; Tetracycline, NAL; Nalidixic Acid, OFX; Ofloxacin and CRO; Ceftriaxone. Graph shows the percentage of resistant (red) and sensitive (grey) organisms isolated from periods A, B and C. Statistical significance was calculated using a chi squared test.

Figure 6

The increasing proportions of antimicrobial resistant S. sonnei and S. flexneri during a fourteen year transition. The distribution of the proportion of S. sonnei and S. flexneri isolates that were resistant to one or more of seven antimicrobials tested. S flexneri strains (red lines) were significantly more likely to be resistant to more antimicrobials that S. sonnei (black lines) over both collections compared. S. sonnei and S. flexneri were significantly more likely to be resistant to more antimicrobials when period C (2007 - 2008) (lines with triangles) was compared to period A (1995 - 1996) (lines with squares).