These research studies have been challenged for the following reasons

• The usage and study of pregnant women with acute kidney infections rather than those suffering from lower urinary tract infections of the bladder and urethra. Kass’s test was never, in its creation, validated for use in lower urinary tract infections for the bladder or urethra.  But it has been readily adopted globally for all infections of the urinary and renal tracts and has not been revised or updated since the 1950s.
• Kass’s belief that the normal bladder is sterile and bacteria introduced via the urethra are the cause of infection. Researchers have refuted that belief in recent years now more is understood about the urinary microbiome (the community of microbes in the urinary tract). Read more about the urinary microbiome. Are infections solely attributable to bacteria and in particular one bacteria introduced into the bladder?  What part do viruses, fungi or other microbes in this urinary soup play?
• Kass also noted that sufferers of a UTI tend to over-dilute their urine by drinking too much water. This means that any sample is not sufficiently concentrated to identify the growth of a single bacterial species let alone multiple infection causing bacteria.
• The failure to recognise polymicrobial infections in Kass’s research (an infection comprising of one or more bacteria) with his belief that the urinary tract infection is caused by a single bacteria. Because of this, samples with multiple organisms or lactobacillus are labelled as ‘contaminated’ or ‘mixed growth’ as it is assumed that these bacteria came from other sources. In reality, these bacteria are not contaminants and may well be contributors to the infection, as in some cases infections can be polymicrobial.
• The culture numbers are likely to depend on the ease of growth of bacteria in a laboratory. Bacterial species react differently to an oxygenated environment. The bacteria residing in your bladder have a limited oxygen source but when a urine sample is placed on a petri dish in the laboratory, the oxygen they are exposed to increases. This means that bacteria which flourish beneficially in this type of environment will grow. An example of this is E-coli whereas those that prefer the ecosystem and oxygen levels of the bladder will grow in limited numbers and are often dismissed as contamination.
• The standard urine culture also does not pick up on viral or fungal causes of infection, which have been proven to be the cause for certain symptomatic patients with negative culture tests, even in patients that are not immunocompromised.
• The E. coli focused design of a standard culture could explain our current E. coli centric view of UTI we have today, since so many other organisms remain undetected. Indeed in one study that analysed 157,000 urine samples using a different technology, E.coli was the dominant species in only 28% of cases.