Haemophilus influenzae is reported as a rare urinary tract pathogen in adults [1-5]. It is a small gram-negative rod and part of the normal bacterial flora in the human upper respiratory tract; strains may possess a polysaccharide capsule or be non-capsulated. The capsular strains are divided into six serotypes (a-f) based on their polysaccharide capsule whereas the non-capsular lack the polysaccharide capsule and are often less virulent. H. influenzae species usually causes upper respiratory tract infections, otitis media, pneumonia and exacerbation of chronic obstructive pulmonary disease. Less frequently, they give rise to invasive disease such as sepsis and meningitis [6, 7]. Here, we report a case of septicemia with a non-capsulated H. influenzae strain isolated from blood and urine in a 32-year old man with bilateral renal stones.

A 32-year old man was admitted to a Danish hospital due to right sided flank pain of four days duration. He had no confirmed medical diagnoses, but had previously been tested for Sarcoidosis, Polycythemia vera, stroke and acute coronary syndrome. He also had a history of former steroid-use. The available medical records did not state his vaccination status or previous childhood infections. At hospitalization, he presented with intermittent right sided flank pain, turning into constant pain of VAS 7-8 and radiating to the right side groin. Additional symptoms were nausea, chills, and observation of blood in the urine. Physical examination revealed right sided abdominal and renal pain and a temperature of 38.0 degrees Celsius. His urine tested positive for leucocytes, erythrocytes, nitrite and protein 1 g/L and blood samples showed normal urate levels, elevated ionized calcium levels 1.56 mmol/L, creatinine 122 µmol/L, leukocytosis of 15.9 x 10⁹ /L and CRP 6.4 mg/L increasing to 172 mg/L the next day. CT scan showed bilateral nephrolithiasis as well as right side ureterolithiasis causing obstruction Fig. (1). Direct microscopy on three out of three blood culture bottles revealed small gram-negative pleomorphic rods within 24 hours of incubation. Mass spectrometry (Bruker Daltonics using MBT Compass software version 4.1 that contains 6903 MSP´s) identified the strain as H. influenzae with a score of 2.24. Microbiology testing of urine routinely cultured on a 5% blood agar plate and a UTI chrome agar plate showed 10⁵ growth of H. influenzae confirmed by MALDI-TOF MS (score of 2.15). The strain was found to be a non-capsulated biotype II, susceptible to all antibiotics tested by disc diffusion: penicillin (1 unit, zone diameter: blood = 15 mm, urine = 15 mm), amoxicillin-clavulanate (3 µg), ampicillin (10 µg), ciprofloxacin (5 µg, zone diameter: blood = 35 mm, urine = 41 mm), cefuroxime (30 µg) and piperacillin-tazobactam (36 µg) using EUCAST disc diffusion recommendations. After microbiology samples had been collected, the patient started antibiotic treatment with intravenous ampicillin 1 g x 4 daily and a right sided JJ ureteric stent was surgically inserted. The patient received two doses of ampicillin, but due to subjective discomfort, treatment was changed to cefuroxime 1500 mg x 3 daily. After three days, the patient was discharged with 5 days of peroral ciprofloxacin 500 mg x 2 and a scheduled ambulant stone-removal surgery.

Fig. (1). Computed Tomography (CT) scan showing bilateral renal calculi and right sided ureteral calculus (arrows).

H. influenzae Invasive Bacterial Disease (IBD) has especially been related to encapsulated strains, mainly serotype b strains causing septicemia, meningitis or epiglottitis. After introduction of Hib vaccination in the childhood vaccine program, episodes with meningitis and epiglottitis have declined to very few cases annually in Denmark [8]. Invasive disease caused by encapsulated strains belonging to other serotypes do occur. However, there is an increasing trend of infections due to non-capsular strains. Hib vaccination does not give protection against infection with such strains. The latest Epidemiological Report, made by the European Centre for Disease Prevention and Control (ECDC), states that in 2014, 2799 confirmed H. influenzae IBD cases were reported (29 countries) [8]. When dividing by serotype it was found that by far the greatest number of cases were caused by non-capsular strains in all age groups (1706 cases, 20 countries) [8]. The highest rates of invasive disease were in children < 1 year old and the elderly with the age of > 65 years, thus, age groups more prone to infectious disease [8]. The most common clinical presentation in this post-Hib vaccine era is pneumonia and septicemia [8, 9]. Our case however was a young immunocompetent man with a urinary tract infection and septicemia. Seldomly, cases of H. influenzae invasive disease with recognized foci outside the respiratory tract occurs. H. influenzae has been reported as the causative agent of acute pyelonephritis [2, 3], chronic prostatitis [10], endometritis [11] and the H. influenzae species has been isolated from urethra in men with symptomatic urethritis [4]. During a 15-year study period, Christensen J.J. et al. isolated Haemophilus species from different unusual sites such as gynaecological or gastrointestinal sites as well as soft tissue and bone and muscle tissue [12]. Specimens from 80 patients were included and 17 isolates were in pure culture. Nine of these were from the Bartholin’s glands, salpinges or parametrium.

In this case, non-typable H. influenzae biotype II was isolated from blood and urine and associated with renal stone disease in a young male patient. He had no respiratory symptoms or alternative focus. Usually, urinary tract infections are caused by Enterobacteriaceae such as E.coli, Klebsiella, Proteus and Serratia species, and less frequently Pseudomonas aeruginosa. Fujii et al. recently reported a similar case of a 46-year old man with biotype III bacteremic pyelonephritis and unilateral ureteral stone [3]. In children, H. influenzae urinary tract infections are rare and possibly associated with abnormalities of the urinary tract [13, 14]. A retrospective study, over a 24-year period, found 36 children out of 5000 urinary tract episodes, with H. influenzae or H. parainfluenzae bacteriuria, equivalent to < 1% of the episodes, and the majority of the children had a urinary tract abnormality and/or renal damage [13]. Thus, we argue that H. influenzae urinary tract infections could be associated with urinary tract or renal disease in adults, as well as children. A proposed link between stone disease and H. influenzae bacteriuria could be the urease activity of the bacteria resulting in ammonia synthesis. This increases the pH of the urine and possibly creates a more favorable environment for bacterial growth as well urolithiasis formation [15]. In addition, it has been demonstrated that non-typable H. influenzae from clinical isolates are able to form biofilm [16] which may increase the risk of chronic infection, facilitate further urolithiasis and increase the resistance to antibiotic treatment.

The isolated strain in our case was susceptible to all antibiotics tested with no recognized resistance mechanisms present. However, the emerging antibiotic resistance in recent years against ampicillin and several other antibiotics among strains of H. influenzae gives cause for serious concern [17, 18]. Epidemiological studies indicated that 8% to 30% of isolates in Europe and North America, and up to around 50% of isolates in East Asia were resistant to ampicillin [17-19]. The recognized resistance mechanisms are beta-lactamase production and PBP3 alterations by mutation [17, 20]. A Korean study of 540 isolates from respiratory tract infections, predominantly non-typable, showed ampicillin resistance of 58% and beta-lactamase production in 52.4% of the isolates [17]. In Canada, a study of 882 isolates of invasive disease demonstrated an increase in beta-lactamase production from 2007 to 2014 and an increasing trend of significant PBP3 mutations [20]. Therefore, when recognizing a serious invasive infection caused by a H. influenzae strain the possibility of eventual antibiotic resistance has to be taken into consideration in the initial treatment recommendation.

Growth of H. influenzae requires growth factor X (heme) and factor V (NAD). For their detection, it is crucial using culture methods accommodating these needs, which is not always done when examining urine specimens. This may lead to an underestimation of occurrence of H. influenzae in urine samples. In our case identification was done using MALDI-TOF mass spectrometry. In a recent study on identification of respiratory pathogens, including 64 H. influenzae strains, by conventional phenotypic methods and mass spectrometry [21], it was shown that mass spectrometry provides identification of these bacteria faster and in a more reliable way than those based on conventional phenotypical methods [21].

To our knowledge, this is the first European report on non-capsulated H. influenzae as etiology of an invasive urinary tract infection associated with renal stones in an immunocompetent young adult. In this post-Hib vaccine era, non-capsulated H. influenzae strains causes the majority of invasive H. influenzae infections. H. influenzae may be an underestimated cause of urinary tract infections and should be kept in mind in culture-negative urinary tract infections, especially when urinary tract abnormalities are present. The emerging antibiotic resistance in recent years against ampicillin and several other antibiotics among strains of H. influenzae has to be taken into consideration when determining initial antibiotic treatment of invasive disease.