Cystitis is an infection of the bladder. It is classified as complicated or uncomplicated. The latter refers to a lower urinary tract infection in men or non-pregnant women who are healthy and have no co-morbidities. On the other hand, complicated cystitis is associated with the presence of concomitant risk factors that increase the likelihood and danger of infection or the chances of failure of antibiotic therapy. Acute cystitis is usually caused by a bacterial infection of the bladder. In women, there is an increased risk of developing an infection due to the close proximity of the rectum to the opening of the urinary canal, as well as the relatively shorter length of the latter. In 75% to 95% of cases, Escherichia coli is the most common cause of cystitis in women, followed by Klebsiella. Other common pathogens include species of the Enterobacteriaceae family, such as Proteus mirabilis, as well as other bacteria, Staphylococcus saprophyticus and Enterococcus. The incidence of antibiotic resistance in complicated infections is also significantly higher. Known resistant organisms include ESBL-producing extended-spectrum beta-lactamase bacteria, as well as carbapenem- and fluoroquinolone-resistant microorganisms, especially E. coli. The incidence of uncomplicated cystitis in men is relatively low. It is estimated that fewer than 10 in 10,000 men under the age of 65 are affected annually. Symptoms of an uncomplicated infection in men are similar to those in women: dysuria, frequent urination, urgency and suprapubic pain – pain located low in the abdomen. Repeated symptoms or re-infections after treatment, fever and pain in the pelvis or perineum are signs of prostatitis. Fever, chills, flank pain, or any symptoms of a systemic illness are signs of a complicated urinary tract infection. Cystitis usually develops due to the colonization of the periurethral mucosa by bacteria from the fecal or vaginal flora and the passage of these pathogens into the bladder. Uropathogens may possess microbial virulence factors that confer resistance to host defense mechanisms and allow colonization of urinary tract tissues. Urinary tract infections in men are much less common because of the greater length of the urethra, the drier periurethral environment, and the antibacterial protection provided by the prostatic fluid. All urinary tract infections in men are considered to be complicated. Major host factors largely determine the pathogenesis of complicated urinary tract infections. Disorders in the function of the immune system, as well as difficulties in urination, which are observed as a result of autonomic neuropathy in diabetics, are a predisposing factor to the development of urinary tract infections. In renal failure, the accumulation of uremic toxins can reduce the host’s defenses,and decreased renal blood flow impairs the ability to eliminate bacteria. Kidney stones can cause blockages in the urinary tract and provide a potential source of infection. In the setting of urinary catheterization, internal and external biofilms can form on the catheter, allowing pathogens to multiply in the bladder. What are the symptoms of cystitis? Dysuria – discomfort, burning and pain during urination; Suprapubic pain; Cloudy urine; Hematuria – presence of blood in the urine. In elderly people, in addition to the characteristic symptoms, there is also an altered mental status, lethargy and generalized weakness. The presence of a strong-smelling and/or cloudy-looking discharge without reporting other symptoms is insufficient to diagnose a lower urinary tract infection or to initiate antibiotic treatment. References: https://www.ncbi.nlm.nih.gov/books/NBK459322/