Globally, there are an estimated 1.7 billion cases of diarrheal disease every year.1 Furthermore, diarrheal disease kills around 760,000 children each year, and it is the leading cause of malnutrition in children under five years old.1 Gastroenteritis can be caused by a wide number of infectious bacterial, viral, and parasitic agents but, due to similar presentation, it is often challenging to correctly diagnose the causative agent on clinical signs and symptoms alone.
Diarrheal disease imparts a high degree of morbidity and mortality in select populations and inflicts a significant toll on the healthcare system. In 2010, the cost for the more than 237,000 patients who were hospitalized suffering from gastrointestinal infections in the U.S. exceeded $6 billion.2 Because of the diagnostic challenges, about 80% of all causes of diarrhea currently go unidentified. This surely must result in a large number of instances of inappropriate treatment.3
Current testing to diagnose the many potential causes of infectious diarrhea is often spread across multiple laboratories, involves multiple testing methods with varying levels of clinical performance, and contributes to long turnaround times that hamper proper patient care. The stool specimen often arrives in the Microbiology laboratory, where it is split for subsequent testing across Microbiology, Virology, and Molecular laboratories. Clinical laboratories may also send out specimens to a reference laboratory for additional tests. Personnel must be extensively trained to perform different types of assays (e.g., culture, EIA, PCR). Each individual test result does not contribute much diagnostic value, and the sensitivity and specificity of tests are limited. In addition, collection of results from these different laboratories and tests often takes multiple days, sometimes weeks. See Figure 1 for an overview of conventional testing and the average time to result.
Figure 1. Conventional GI testing requires results from multiple laboratories that can take two to three days to be completed.
During the last four or five years, syndrome-based molecular testing has revolutionized respiratory testing by allowing physicians to have a more comprehensive picture of respiratory infections. Now, rapid molecular multiplex testing is being introduced into enteric diagnostics. The FDA has recently cleared molecular multiplex tests affording simultaneous detection and identification of multiple gastrointestinal bacterial, viral, and parasitic pathogens from a single patient sample.4 Due to the multiplexing capabilities and short turnaround time, these new molecular methods have the potential to revolutionize patient diagnosis and treatment for diarrheal disease.
Recent peer-reviewed articles describe the performance and clinical utility of the multiplex molecular panel approach to diagnosis of gastrointestinal infections. Malecki and co-workers described the molecular methods which were essential for detection of Escherichia coli O104:H4 and novel diarrheagenic E. coli strains appearing during the outbreak in Germany in 2011.5 The microbiological methods available at that time were unsuitable to accurately identify the outbreak, and rapid screening diagnostic methods were essential to ensure timely and appropriate patient management.
Kahlau et al.6 evaluated rapid multiplexed molecular techniques as a frontline test for gastroenteritis with 347 stool samples from adult hospitalized patients and demonstrated their utility as compared to conventional microbiological methods. One hundred fifty-seven of the samples were found to be positive for at least one pathogen, and the panel approach significantly reduced the time to the initial identification of a pathogen. Moreover, molecular testing detected additional pathogens that were not requested by the physician, and thus may be an important tool for avoiding nosocomial outbreaks.
Diarrhea is a frequent complication in transplant patients; when microbiological examination is negative, this is attributed to adverse effects of immunosuppressive therapy. Coste et al.7 describe the improvement of microbiological diagnosis and management of diarrheic kidney transplant patients through implementation of molecular testing. Fifty-four severe diarrhea events occurring in 49 adult kidney transplant recipients were investigated. One or several enteric pathogens were detected in 72% of stool samples by the seven commercially available multiplex PCR assays tested, as compared to only 23% using classical microbiological techniques. Enteropathogenic E. coli (EPEC), Campylobacter spp., and norovirus were the most common pathogens (36% to 38%), and based on molecular findings, cyclosporin and mycophenolate mofetil combination therapy was identified as a risk factor of developing norovirus diarrhea.
Mengelle and co-workers tested 440 stool samples (including 102 adult immunosuppressed, 50 pediatric immunosuppressed, 56 neonatal, and 121 pediatric emergency patients) using a multiplexed molecular panel, and from 176 samples found 162 patients positive for viruses (23.2%), bacteria (13.9%), or parasites (2.9%).8 The majority of positive samples (92.6%) were from children attending the emergency unit. The molecular assay was significantly more sensitive than the conventional tests for detecting rotavirus, noroviruses, Salmonella spp., Campylobacter spp., and toxigenic Clostridium difficile.
Because patients with gastroenteritis present with similar signs and symptoms, doctors rely on diagnostic testing to help identify the causative pathogen and help guide therapeutic treatment. The hard lines in etiology separating community-acquired from hospital-acquired diarrhea are rapidly deteriorating. Recent reports suggest that possibly one-third of C. difficile infections are being acquired in the community.9 Moreover, noroviruses infect tens of millions of Americans each year, and are especially on the rise in children;10 however, norovirus is rarely tested for despite the massive infection control concern in outbreak situations.11 Using a single comprehensive molecular assay aids laboratories and physicians to screen out both suspected, and more importantly, unsuspected causes of diarrhea to get ahead of potential outbreak scenarios.
References
- Diarrhoeal Disease, Fact sheet N°330. World Health Organization. http://www.who.int/mediacentre/factsheets/fs330/en/index.html. Accessed June 20, 2013.
- National Statistics on Intestinal Infections (2010). U.S. Dept. of Health and Human Services HCUPnet. http://hcupnet.ahrq.gov/HCUPnet.jsp. Accessed June 26, 2013.
- CDC Estimates of Foodborne Illness in the United States. Centers for Disease Control and Prevention. http://www.cdc.gov/foodborneburden. Accessed June 26, 2013.
- FDA permits marketing of first test that can simultaneously identify 11 causes of infectious gastroenteritis. U.S. Food and Drug Administration. http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm335274.htm Accessed June 26, 2013.
- Malecki M, Schildgen V, Kamm M, Mattner F, Schildgen O. Rapid screening method for multiple gastroenteric pathogens also detects novel enterohemorrhagic Escherichia coli O104:H4. Am J Infect Control. 2012;40(1):82-83.
- Kahlau P, Malecki M, Schildgen V, et al. Utility of two novel multiplexing assays for the detection of gastrointestinal pathogens – a first experience. SpringerPlus. 2013;2(1):106.
- Coste JF, Vuiblet V, Moustapha B, et al. Microbiological diagnosis of severe diarrhea in kidney transplant recipients using multiplex PCR assays. J Clin Microbiol. 2013;51(6):1841-1849.
- Mengelle C, Mansuy JM, Prere MF, et al. Simultaneous detection of gastrointestinal pathogens with a multiplex Luminex-based molecular assay in stool samples from diarrheic patients. Clin Microbiol Infect. 2013. doi: 10.1111/1469-0691.12255. [Epub ahead of print].
- Leffler DA, Lamont JT. Editorial: Not so nosocomial anymore: the growing threat of community-acquired Clostridium difficile. Am J Gastroenterol. 2012;107(1):96-98.
- Chhabra P, Payne DC, Szilagyi PG, et al. Etiology of viral gastroenteritis infections in children J Infect Dis. 2013. [Epub ahead of print].
- Greig JD, Lee MB. A review of nosocomial norovirus outbreaks: infection control interventions found effective. Epidemiol Infect. 2012;140(7):1151-1160.
