The burden and characteristics of enteric fever at a healthcare facility in a densely populated area of Kathmandu

Abstract

Enteric fever, caused by Salmonella enterica serovars Typhi and Paratyphi A (S. Typhi and S. Paratyphi A) remains a major public health problem in many settings. The disease is limited to locations with poor sanitation which facilitates the transmission of the infecting organisms. Efficacious and inexpensive vaccines are available for S. Typhi, yet are not commonly deployed to control the disease. Lack of vaccination is due partly to uncertainty of the disease burden arising from a paucity of epidemiological information in key locations. We have collected and analyzed data from 3,898 cases of blood culture-confirmed enteric fever from Patan Hospital in Lalitpur Sub-Metropolitan City (LSMC), between June 2005 and May 2009. Demographic data was available for a subset of these patients (n = 527) that were resident in LSMC and who were enrolled in trials. We show a considerable burden of enteric fever caused by S. Typhi (2,672; 68.5%) and S. Paratyphi A (1,226; 31.5%) at this Hospital over a four year period, which correlate with seasonal fluctuations in rainfall. We found that local population density was not related to incidence and we identified a focus of infections in the east of LSMC. With data from patients resident in LSMC we found that the median age of those with S. Typhi (16 years) was significantly less than S. Paratyphi A (20 years) and that males aged 15 to 25 were disproportionately infected. Our findings provide a snapshot into the epidemiological patterns of enteric fever in Kathmandu. The uneven distribution of enteric fever patients within the population suggests local variation in risk factors, such as contaminated drinking water. These findings are important for initiating a vaccination scheme and improvements in sanitation. We suggest any such intervention should be implemented throughout the LSMC area.

Figure 1. Enteric fever case burden in patients attending Patan Hospital, 2005–2009.

Plot showing the number of culture positive enteric fever cases at Patan Hospital per month between June 2005 and May 2009 (solid black line; S. Typhi and solid grey line; S. Paratyphi A). The broken black line shows the number of patients attending the outpatient department per month over the same period, with numbers in grey boxes equating to the annual number of blood cultures performed.

Figure 2. The seasonal distribution of enteric fever patients at Patan Hospital.

Plot of the seasonal distribution of enteric fever patients at Patan Hospital in Kathmandu. The average number of S. Typhi cases (black line) and S. Paratyphi A cases (grey line) for each month of the year was calculated over the period June 2005–May 2009. Vertical lines represent the range over the four year period for each month. The average monthly rainfall (mm) is shown by the broken black line and corresponds with the secondary y axis.

Figure 3. The distribution of enteric fever cases in LSMC.

Maps depicting the average annual incidence of enteric fever per 1,000 population in the 22 wards (numbered) that constitute the Lalitpur Sub-Metropolitan City (LSMC), based on enteric fever cases enrolled in clinical trials at Patan Hospital between June 2005 and May 2009 for (a) S. Typhi and b) S. Paratyphi A). Patan Hospital is located in ward 20 and is highlighted. Ward population figures are presented in Table 1.

Figure 4. The age distribution of a subset of enteric fever cases at Patan Hospital, LSMC.

A double sided bar chart showing the age distribution (central scale; y axis) of blood culture positive enteric fever cases enrolled in clinical trials at Patan Hospital in LSMC between June 2005 and May 2009 (n = 527). Bar sizes correspond to the number of patients (upper x axis) of each sex (left; male and right; female). Cases that were culture positive for S. Typhi are shown in dark shading, those that were culture positive for S. Paratyphi A are shown in light shading. The ratio of culture positive S. Typhi to S. Paratyphi A cases over the period of investigation in each five year age group for males and females are shown by the solid lines with solid circles (lower x axis). The overall ratio of S. Typhi to S. Paratyphi A was 2.69∶1 in males (shown by the black broken line a) and 2.73∶1 in females (shown by the black broken line b). The median age of the male and female patients is shown by the asterisk.