What are the key concepts related to horizontal versus vertical safety programs in infection control?

The key concept is that horizontal programs seek to reduce all infections at a given anatomic site (all pathogens), whereas vertical programs focus on reducing single pathogens (e.g., methicillin-resistant Staphylococcus aureus [MRSA] surgical site infections). Horizontal programs, if effective, have a greater impact because they target a larger proportion of infecting agents. Edmond has emphasized recently that vertical programs have a brief time horizon for infection control, whereas horizontal programs have a long view. Importantly in this author’s view, horizontal programs will prevent not only currently endemic infections but also the rapid rise of the initially unrecognized, emerging, causes of health care-associated infections. For all infection control programs, a horizontal program must form the platform on which selective vertical programs are integrated.

What principles need to be adhered to for effective infection control?

The use of evidence-based bundles, including “check lists” related to managing devices, has been effective in reducing infections broadly and significantly. Recently, a horizontal program in the operating room, substitution of the surgical scrub from an iodophor to chlorhexidine-alcohol preparation, reduced the total surgical site infections, all pathogens, by 40%. Furthermore, without an associated vertical program, the better performing preoperative skin preparation was associated with a 50% reduction of Staphylococcal surgical site infections.

What are the conclusions of clinical trials or meta – analyses regarding horizontal versus vertical safety programs in infection control?

With respect to MSSA and MRSA, vertical programs do work in preventing surgical site infections. Recent data showed a 60% reduction of S. aureus surgical site infections associated with the institution of preoperative nasal decolonization with mupirocin plus daily baths with chlorhexidine alcohol among carriers. However, there is insufficient information related to MRSA at other anatomic sites. A critical point is that so far, no vertical intervention program has shown a significant reduction in total infection rates.

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In contrast to outcomes of vertical programs, horizontal programs in general have been effective in reducing rates by at least 40% for surgical site infections, ventilator associated pneumonias, and catheter related urinary tract infections. What is remarkable is that even in the absence of a vertical program for MRSA, the horizontal process at the Medical College of Virginia Hospital reduced infections caused by MRSA by approximately 50%.

Of interest related to surgical site infections, if one were to combine the horizontal and the vertical programs to prevent surgical site infections, the vertical program with screening for S. aureus carriage and treating carriers would complement the horizontal program with the chlorhexidine alcohol scrub by adding an additional 7.5% reduction in total infections. The combined 47.5% possible reduction in surgical site infections was unthinkable a decade ago.

What are the consequences of ignoring the key principles and concepts of safety programs in infection control?

Focusing time and resources on ineffective or marginally effective vertical programs may limit the overall impact of a hospital’s horizontal program. The costs for vertical programs appear to be substantial relative to their impact compared to a horizontal program. So resources expended on them have to be based on excellent data showing great value for the additional intervention. Most importantly, failure to institute a horizontal program will have dramatically negative consequences on the total infection rates.

A summary of current controversies regarding horizontal versus vertical safety programs in infection control.

The key principle is that an infection control program must have a strong horizontal program in place. Thereafter, the critical question is, “what is the incremental value of a vertical program above that of a horizontal program?”

The question focuses on the cost and benefit of a new vertical program built on the platform of a horizontal program. Of interest is the fact that an initial vertical program focusing on a single pathogen can be found later to be in fact a horizontal program. An example is that chlorhexidine baths in successive trials have been found to be effective in reducing colonization and infection rates of MRSA, vancomycin-resistant Enterococcus (VRE), and Acinetobacter.

What is the impact of horizontal versus vertical safety programs in infection control?

By definition, horizontal programs will have a much greater impact than vertical programs. Thus, the key issue is when to institute and how to measure the impact of new vertical programs. This can be illustrated from the example of nosocomial bloodstream infections shown in the example below:

If 10 percent of all healthcare associated infections are bloodstream infections, and if the total infection rate is 5 to 10%, there would be 50 to 100 healthcare associated infections expected for a hospital with 10,000 admissions a year. However, only 14% would be expected to be MRSA i.e., 7 to 14 bloodstream infections. If 25% of the patients with bloodstream infections would be expected to die and 50% of the deaths are directly attributable to the infections, then there would be expected to be 7 to 13 total bloodstream related deaths attributed to the infection but only one to two attributed to MRSA.

Now imagine two programs: a horizontal program that could reduce all bloodstream related deaths by 50% (thus saving four to seven deaths per 10,000 hospitalizations), versus a vertical program effective in reducing 50% of MRSA deaths (one death). Translated to the U.S. with approximately 35 million acute care admissions a year, the horizontal program saves 14,000 to 24,500 deaths versus the vertical program that saves 3,500 MRSA related bloodstream deaths.

Similar arguments can be made with the same example that a horizontal program greatly saves years of life lost and direct costs related to infections.

Controversies in detail.

There remain proponents of vertical programs, each of which focus on a formidable hospital pathogen. Initially, most infection control experts called attention to MRSA, in part related to its emergence in the 1980s and 1990s as one of the very few antibiotic-resistant pathogens plaguing hospitals. With the subsequent emergence of VRE, MDR – GNR, and triazole-resistant species of Candida, there are new challenges with limited control data and new costs.

A key criticism, however, has been that none of the proposed vertical programs has been shown to reduce total infection rates. Thus, the benefits cannot be broadly assessed at this time. Of interest, MRSA infection rates nationally began to fall before the institution of vertical programs. The question remains, however, if credit is due to horizontal programs or instead to the natural biological fluctuations of pathogens causing infections in populations.

Since the true value of some vertical programs is not proven, e.g., widespread MRSA screening of all hospitalized patients, is it fair to mandate that these programs be in place in hospitals? This remains an important current controversy, and many states have already enacted laws to mandate screening for MRSA in the U.S. One could argue that the costs are substantial and the reductions expected are no better than one could expect from an effective horizontal program.

None of this is to say that those who advocate for a vertical program for MRSA, VRE, MDR Acinetobacter, etc., are focusing on insignificant pathogens. These are critically important bacteria, but such advocates must show the value of the program in reducing a substantial reduction in total infection rates at a reasonable cost. So far this has not been done: no vertical program so far has shown a significant reduction in the total infection rate in any hospital.


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