The Use of Microarray Technology for Diagnosing Infectious Diseases

Molecular diagnostic techniques for viral testing have undergone rapid development in recent years. They are becoming more widely used than the classical virological assays in the majority of clinical virology laboratories, and now represent a new method for the diagnosis of human viral infections. Recently, new techniques based on multiplex RT-PCR amplification followed by microarray analysis have been developed and evaluated. On the basis of amplification of viral genome-specific fragments by multiplex RT-PCR and their subsequent detection via hybridization with microorganism-specific binding probes on solid surfaces, they allow simultaneous detection and identification of multiple viruses in a single clinical sample. The management of viral central nervous system and respiratory tract infections currently represents the two main applications of the microarrays in routine virological practice.

Microarrays have shown reliable results in comparison with those of referenced (RT)-PCR assays, and appear to be of major interest for the detection of a broad range of respiratory and neurotropic viruses, assessment of the pathogenicity of newly discovered or neglected viruses, and identification of multiple viral infections in clinical samples. Despite several limitations observed during the different studies performed, this new technology might improve the clinical management of patients by enlarging the range of the viruses detected, in particular in cases of severe infections leading to patient hospitalization in the intensive-care unit. They might also help in the prevention of nosocomial transmission in hospital departments by contributing to the development of new epidemiological surveillance systems for viral infections.

References

1. Mikhailovich, V., Gryadunov, D., Kolchinsky, A., Markarov, A., & Zasedatelev, A. DNA Microarrays in the Clinic: Infectious Diseases. PubMed, 10, 673-82.

Burden of Healthcare Associated Infections

The goal of infection control is to eliminate healthcare-associated infections. Estimations of the burden of such infections are generally performed through analyses of surveillance programs, such as the National Healthcare Safety Network of the Centers for Disease Control and Prevention (CDC) in the United States, and are often reported by type of infection.

In the United States, the national burden of healthcare-associated infections overall was estimated through a separate survey in 2011 of over 11,000 randomly selected inpatients from 183 general or pediatric acute care hospitals of varying size across 10 different states. Overall, 504 healthcare-associated infections in 452 patients (4.0 percent of the total surveyed population) were identified. Pneumonia and surgical-site infections were the most common, each accounting for 22 percent of all infections, followed by gastrointestinal, urinary tract, and primary bloodstream infections. Clostridium difficile and Staphylococcus aureus were the most common pathogens identified. Device-associated infections (ie, ventilator-associated pneumonia, catheter-related urinary tract infection, and catheter-related bloodstream infection) together accounted for 26 percent of all infections.

Based on these results and data on national hospital admissions and lengths of stay, an estimated 648,000 hospitalized patients in the United States experienced healthcare-associated infections in 2011. Of note, because of the scope of the survey, this estimate does not include individuals in other institutions, such as skilled nursing or longitudinal care facilities, who are also at risk of such infections. Nevertheless, these findings highlight the substantial problem of health care-associated infections and the importance of infection control measures that target all infections, not just those associated with devices. Beyond the additional morbidity for the individual patient, healthcare-associated infections lead to tremendous financial costs. The high prevalence of multi-drug resistant organisms associated with healthcare-associated infections further adds to the excess morbidity, mortality, and cost. 

References

1. National Healthcare Safety Network. (2013, February 1). Retrieved July 24, 2014, from http://www.cdc.gov/nhsn/.

Scientists find way to trap, kill malaria parasite

 Credit: National Institute of Allergy and Infectious Diseases

The malaria parasite, Plasmodium falciparum, is among the world's deadliest pathogens. Malaria is spread mainly by the bite of infected mosquitoes and is most common in Africa. In 2012, an estimated 207 million cases of malaria occurred worldwide, leading to 627, 000 deaths, according to the World Health Organization. Resistance to drug treatments is spreading among the parasite's many strains, and researchers are working hard to find new drug targets.

Scientists may be able to entomb the malaria parasite in a prison of its own making, researchers at Washington University School of Medicine in St. Louis report July 16 in Nature.

As it invades a red blood cell, the malaria parasite takes part of the host cell's membrane to build a protective compartment. To grow properly, steal nourishment and dump waste, the parasite then starts a series of major renovations that transform the red blood cell into a suitable home.

But the new research reveals the proteins that make these renovations must pass through a single pore in the parasite's compartment to get into the red blood cell. When the scientists disrupted passage through that pore in cell cultures, the parasite stopped growing and died.  

"The malaria parasite secretes hundreds of diverse proteins to seize control of red blood cells," said first author Josh R. Beck, PhD, a postdoctoral research scholar. "We've been searching for a single step that all those various proteins have to take to be secreted, and this looks like just such a bottleneck."

A separate study by researchers at the Burnet Institute and Deakin University in Australia, published in the same issue of Nature, also highlights the importance of the pore to the parasite's survival. Researchers believe blocking the pore leaves the parasite fatally imprisoned, unable to steal resources from the red blood cell or dispose of its wastes.

References

1.Griffin, Catherine. July 2014. Science World Report. Scientists Discover New Method to Trap and Kill Malaria Parasite, Halting Its Spread. http://www.scienceworldreport.com/articles/16085/20140717/scientists-discover-new-method-trap-kill-malaria-parasite-halting-spread.htm. Retrieved July 18, 2014.

Case Answers

1. Based on these clinical findings, what is the likely causative agent?

Clostridium difficile - the exotoxin produces the cellular injury. The responsible microorganisms are typically not seen in tissue section. Diagnosis is made by the detection of toxin.

2. Explain how you were able to identify the organism. 

Based on the images provided, pseudomembrane plaques were observed. Also, she required multiple antibiotics which indicates that her normal intestinal flora was destroyed.

3. Which of the following are appropriate specimen samples for anaerobe culturing:

1. blood, spinal fluid, abscess aspirate
2. deep tissue biopsy, sputum, blood
3. cerebrospinal fluid, tissue and debridement from decubitus ulcer, bile
4. tissue swabs, blood, urine

Clinical Case Study

A 45-year-old woman is being treated in the hospital for pneumonia complicated by septicemia. She has required multiple antibiotics and was intubated and mechanically ventilated earlier in the course. On day 20 of hospitalization, she has abdominal distention. Bowel sounds are absent, and abdominal radiograph shows dilated loops of small bowel suggestive of ileus. She has a low volume of bloody stool.



Here are the 2 images of her small bowel:

  

                            

                  

Questions 

1. Based on these clinical findings, what is the likely causative agent?

2. Explain how you were able to identify the organism. 

3. Which of the following are appropriate specimen samples for anaerobe culturing:

1. blood, spinal fluid, abscess aspirate
2. deep tissue biopsy, sputum, blood
3. cerebrospinal fluid, tissue and debridement from decubitus ulcer, bile
4. tissue swabs, blood, urine