Meningococcal infection is a global problem occurring as sporadic, hyper-sporadic, and epidemic disease [8]. The problem has mainly occurred in the developing world especially in the African meningitis belt where there has been an increased risk of bacterial meningitis characterized by distinct seasonal patterns in disease incidence with peaks in the dry season [11, 18].
In Ethiopia, meningitis outbreaks have been occurred over several years being responsible for morbidity and mortality [12]. Therefore, this study was intended to show the gap and fill the limited information on the oropharyngeal carriage, antimicrobial resistance pattern and associated risk factors for N. meningitidis especially in school children in our study area.
The overall N. meningitidis oropharyngeal carriage rate in this study was 10.1%. The predominant serogroup in our study was serogroup A (24.5%) and W135/Y (20.6%) while the least was serogroup B (7.6%). This overall carriage prevalence was markedly higher than a study conducted at Gondar University teaching hospital in 2012 (234 oropharyngeal swabs) among <10 years OPD patients with 6% carriage [19]. The reason for this variation might be due to the difference in the target population, time of investigation and sample size. Our study also had a high prevalence of carriage than the studies conducted in Arba Minch, Southern Ethiopia among 7479 oropharyngeal samples (PCR method) with 6.6% prevalence [20] and in Gurage Zone, Southern Ethiopia with 4.6% carriage rate [21]. On those mentioned studies, no serogroup A was identified and serogroup B was the least identified. The overall difference might be due to the difference in the target population, sample size, type of sample, the method used and an area of investigation done.
In contrast, our study had less carriage rate compared to three local studies conducted at Gondar university hospital (2019 CSF samples) in the year 2011 to 2013 with 18.4% prevalence [22], Addis Ababa (240 nasal swabs) with 20.4% carriage rate [13] and bacterial meningitis surveillance in Ethiopia, 2012–2013 (139 CSF samples with PCR method) with 19.4% prevalence rate [23]. The predominant serogroups in our study had shown variation with findings in Addis Ababa W-135 [13] and Gondar W-135[23], but in line with the study conducted in Gondar[22]. The variation of the prevalence compared to these three studies might be due to the difference in the type of sample investigated, a period of the investigation, local area, sample size, method used and target population.
Compared to the studies conducted in the African countries, our study had more prevalent isolates than the study conducted in Kaya, Burkina Faso in 2009 (6686 throat swabs) with 6.27% [24]. The variation for this difference might be due to geographic differences, sample size and time of investigation. In contrast, our finding had a less prevalent carriage rate than the study conducted among students in Kano Nigeria, (150 nasal swabs) with 15.3% meningococcal carriage rate [25]. Compared to this study, the predominant serogroup in our study was serogroup A. The overall variation for these differences might be due to sample size and geographic differences.
The prevalence of N. meningitidis in our study had a high carriage rate than three studies conducted in Mali, with oropharyngeal carriage of 5%, 7.7%, and 6.9% [11,26, 27] respectively. The predominant serogroup was none-serogroupabable and serogroup A was not identified. The possible reason for this variation might be the geographic difference.
The present study showed a lower carriage rate compared to meningococcal carriage in Dutch adolescents and young adult (1715 oropharyngeal swabs detected by rt-PCR) with 15.6% [28], besides, most common serogroup identified was B. The difference might be due to geographic location, sample size and method used. In contrast; our finding was six times higher prevalence than a study conducted on healthy Dutch children aged 1–19 years (3098 nasal swabs) which had a 1.5% meningococcal prevalence with serogroup B and C were predominant [29]. This variation might be due to the difference in the geographic area and time of investigation.
In this study, meningococcal carriage rate had lower prevalence than the study conducted in the 11-18 year age group with 13.9% prevalence in the United Kingdom [30]. The variation might be due to geographic area differences and method used for identification (ELISA).
The meningococcal carriage rate in our study was higher than the study conducted in Chile in 2013 (4217 throat swabs) from 10-19 years children & adolescents with a 6.5% carriage rate with serogroup B was the predominant [31], this variation might be due to geographic difference, time investigation and sample size. In the present study, meningococcus prevalence was higher than the study conducted in Turkey in 2002 in the age 7-14 years of 1128 primary school children with 6.2% prevalence, with serogroup C more prevalent than others [7]. The possible reason for this variation might be geographic area difference sample size and time of the investigation.
In our study, the prevalence of N .meningitidis was in line with the study conducted in Brazil with 9% [32] and 9.9% meningococcal prevalence [33] and, a study conducted in Kashan Iran, with 8.9% carriage [34]. However, our study had two times higher prevalence rate than the study conducted among students aged 11-19 years with a 4.9% meningococcal prevalence in Brazil [35]. The serogroup findings in our study were different from these study findings. The possible reason for the variation might be due to geographic area differences and methods used.
The antimicrobial susceptibility pattern of N. meningitis was determined. In the present study, higher resistance was reported for cefotaxime (35.8%), ciprofloxacin (45.3%) and trimethoprim-sulfamethoxazole (73.6%). The possible reason for increasing resistance was due to the easy accessibility of drugs, the simplicity of taking drugs (oral route of administration) and the use of these antibiotics for a long period of time in the country especially ciprofloxacin and trimethoprim-sulfamethoxazole and on top of that, irrational drug use. The study conducted in Gondar reported the highest resistance rates of N. meningitidis against cotrimoxazole (100%) and ceftriaxone (50.0%) [19]. In contrary to our study, in Addis Ababa [13] and Gondar [19], N. meningitides was susceptible to ciprofloxacin with the rate of 83.7% and 78.6% respectively. This discrepancy might be due to the difference in the period of investigation.
However, most bacterial isolates were sensitive to azithromycin (96.2%), chloramphenicol (92.5%), minocycline (88.7%) and meropenem (84.9%). This was inconsistent with the study conducted at Gurage zone with minocycline (92%), meropenem (89%) and azithromycin (95%) [21]. The highest sensitivity to azithromycin in the present study might be due to the expensiveness of the cost of the drug that every individual could not access easily, while chloramphenicol might not be routinely administered due to bone marrow depression effect and minocycline is currently not in use in Ethiopia. In the present study, the multidrug resistance pattern of N. meningitidis was higher compared to 14.3% in Addis Ababa [13] and 54.5% in Gurage zone Ethiopia [21]. This result noted that N. meningitides is developing a resistance to the antibiotics through time.
In the present study, independent variables like living in large family size, sharing drinking and eating utensils, history of tonsillectomy, history of visiting healthcare institutions, indoor cooking, parental cigarette smoking and the number of students per classroom were significantly associated with N. meningitidis oropharyngeal carriage.
In our study, history of students with tonsillectomy is significantly associated with meningococcal carriage (P = 0.006). Because of removal of uvula decreases the effectiveness of innate immunity around the oropharynx. Uvula helping to recognize mucosal surface antigens, like bacteria, virus and fungal elements and is the immune response to clear them from the body. Another risk factor that significantly associated with meningococcal carriage in this study was large family size living together (P = 0.003). In different studies, the number of family members [34], crowded living condition [13, 36], the number of children living in the house [31], the number of positive household members [33], lower socioeconomic status [30] and overcrowding in the house [35] were significantly associated risk factors in which coincided with our study finding. As family size increase per house, it leads to low socioeconomic condition that results in low immunity and overcrowding by itself promotes a high rate of respiratory tract infection transmission.
In the present study, parental cigarette smoking was identified as a risk factor for the colonization of N. meningitidis (P = 0.004). A study conducted in Chile among children and adolescents aged 10-19 identified the number of smoking cohabitants and smoking were independent risk factors for oropharyngeal colonization of N. meningitides [31]. In another study, participants mothers or siblings smoked cigarettes [36] and passive smoking [33] were identified as significant risk factors for colonization. Active and passive smoking damages the upper layer of the mucosal surface of the respiratory tract, which favors the colonization of bacteria.
In our study, another identified risk factor for meningococcal colonization was; the study participants history of visiting health care institutions (P = 0.031) and number of students per class greater than 40 (overcrowding) (P = 0.048). In different studies, attending in areas that people visited crowded area was stated as risk factor for meningococcal carriage. A study conducted in Dutch describe youth-club visits for 13 hours per week and discotheque visits for 13 hours per week [29] and a study from Brazil, attendance of night clubs and learning at public school [33], a study from Wales, social gatherings and number of students per class [37] were significant risk factors for the colonization of N. meningitidis. Attending in areas that people gathering is an important factor for the transmission of respiratory transmitted infections. It might be due to a large number of students in one class room makes them more frequent contact among each other, overcrowding and greater sharing of aerosol droplets which cause the more spread of the bacteria.
Indoor kitchen location (P = 0.009) was another independently associated risk factor for the colonization of meningococcus in our study which in line with the study conducted in the African meningitis belt countries, kitchen location (indoor) was significantly associated risk factor [36]. Family member share utensils for drinking and eating (P = 0.007) were statistically significant to the meningococcal oropharyngeal carriage in our study, even though it not stated in another study. The possible reason might be utensils carry oral droplets and transfer from carrier individual to another that fasten meningococcal colonization.