Impact of Mycoplasma pneumoniae coinfection in children with adenovirus pneumonia


 Background Since the winter of 2018 to the end of 2019, there has been an epidemic of Adenovirus infection in southern China, including Zhejiang province, and the number of children suffering from adenovirus pneumonia has increased significantly. Adenovirus pneumonia is often accompanied by other infections in children[3,4], but the effect of other Pathogenic coinfection on the AP has been reported few. Mycoplasma pneumoniae is also an important pathogen of community-acquired pneumonia, accounting for 20-40% of children's CAP[5]. As we know the Impact of Mycoplasma pneumoniae coinfection in children with adenovirus pneumonia, which has drawn the attention of the society and the Paediatrician now has not been reported before. This study aimed to investigate the impacts of MP coinfection on hospitalized AP patients, to identify the risk factors for those patients. Methods Nasopharyngeal swabs (NPSs) or sputum specimens for Culturing were collected from patients once they were admitted to our hospital. ADV-Ag, MP-IgM and MP nucleic acid was tested at the same time, then we classify under two groups(single AP groups and AP groups coinfected with MP) . The clinical manifestations, laboratory and imaging findings and clinical medication of the two groups were compared and analyzed.Results A total of 171 patients diagnosed with single AP and 125 patients diagnosed with AP coinfected with MP. Coinfection group lead to a significantly longer duration of fever than single AP group(p=0.03). Shortness of breath was more commonly found in the coinfection group(P = 0.023).there was no statistical difference in pulmonary signs and blood tests between the two groups (P > 0.05). pulmonary imaging, such as pulmonary consolidation, atelectasis, pleural effusion and multi lobe lesions were more common in the coinfection group (P < 0.05). The patients with coinfection had a more severe symptom, leading to a significantly longer hospitalization time, and increasing the proportion of patients using glucocorticoids and / or gamma globulin, needing oxygen inhalation(P < 0.05). Conclusions The occurrence of adenovirus pneumonia coinfected MP is high. prediction factors of prolonged fever duration and pulmonary imaging can be used to predict MP coinfection in children with adenovirus pneumonia. AP patients coinfected MP may easily turn into severe illness, and a reasonable change in treatment is necessary.


Introduction
Since the winter of 2018 to the end of 2019, there has been an epidemic of Adenovirus infection in southern China, including Zhejiang province, and the number of children suffering from adenovirus pneumonia has increased signi cantly, which has drawn the attention of the society and the Paediatrician.
Adenovirus pneumonia (AP) is an important pathogen of community-acquired pneumonia (CAP) in children, accounting for 4~10% of CAP in hospitalized children [1]. In severe cases, the manifestations of persistent high fever, severe cough and progressive exacerbation of lung lesions may occur, furthermore Chronic airway diseases such as bronchiolitis obliterans may have been long existed. In recent years, more and more attention has been paid to the in uence of adenovirus in respiratory tract infection in China [2].
Adenovirus pneumonia is often accompanied by other infections in children [3,4], but the effect of other Pathogenic coinfection on the AP has not been reported before. Mycoplasma pneumoniae is also an important pathogen of community-acquired pneumonia, accounting for 20-40% of children's CAP [5]. Our study found that Mycoplasma pneumoniae is one of the main pathogens of coinfection of adenovirus pneumonia in children, and the purpose of this study was to investigate the impacts of MP coinfection on hospitalized AP patients, to identify the risk factors for those patients.

Subjects:
The study was performed from January 1 to December 31, 2019, at Hangzhou children's hospital, a tertiary care hospital in Zhejiang. 171 cases of single adenovirus pneumonia and 125 cases of coinfected with Mycoplasma pneumoniae were collected during the year.

Inclusion criteria
Patients was enrolled according to the inclusion criteria: (1) age between 29 days and 18 years old; (2) Patients with AP were diagnosed according to the guidelines for the diagnosis and treatment of adenovirus pneumonia and community-acquired pneumonia in children (2019 version) in China [2,6]; (3) positive detection of ADV antigen in nasopharyngeal secretion. (4) positive detection of MP IgM or MP nucleic acid of throat swab or sputum was positive.

Methods
Nasopharyngeal swabs (NPSs) or sputum specimens for Culturing were collected from patients once they were admitted to our hospital. ADV-Ag, MP-IgM and MP nucleic acid was tested at the same time.
The medical records of each patient, including demographic data, clinical features, laboratory tests(including some kinds of pathogens, such as In uenza virus-Ag and RSV-Ag) and radiological results, were obtained. The study was approved by Hangzhou Children's Hospital Ethics Committee, and written informed consent was obtained from the parents of each patient. The clinical manifestations, laboratory and imaging ndings and clinical medication of the two groups were compared and analyzed.

Statistical analysis
The measurement data in accordance with normal distribution was expressed as± s, t-test was used to compare groups. M (range) was expressed for unnormal distribution measurement data, Rank sum test was used for inter group comparison. counting data was expressed as No. (%) and comparisons were made using χ2 test. A P value< 0.05 was considered statistically signi cant. Analyses were performed using SPSS v20.0

Clinical characteristics of patients
Totally 65,659 times of Adenovirus Antigen were detected during the year, 5161 cases (7.9% 5161/65659) were positive for adenovirus, and 308 cases (6.0% 308/5161) were diagnosed as adenovirus pneumonia. 137 patients in the 308 cases were coinfected with other pathogens, including mycoplasma pneumoniae(125 cases), in uenza virus(5cases), Streptococcus pneumoniae(1 cases), Haemophilus in uenzae(2 cases), The overall coinfection rate was 44.48%. MP was the most prevalent organism, accounting for 40.58%. Two or more pathogens were detected in 3 patients, including mycoplasma pneumoniae and in uenza virus(3cases), mycoplasma pneumoniae and Haemophilus in uenzae(1 cases). Among the 308 patients, a total of 171 patients diagnosed with single AP, average aged 3.04 years, were enrolled in our study. Of these, 116 patients were male; On the other hand, there were 125 patients diagnosed with AP coinfected with MP, with a median age of 3.83 years. 73 cases were male in the coinfected group. The age of the coinfection group was older than the single AP group (P = 0.004), but there was no signi cant difference between the two groups in gender(P=0.095). The incidence rate in the AP groups was the highest in spring, however in coninfection group it was in summer, there was signi cant difference in seasonal incidence rate between the two groups (P = 0.013). The general characteristics of all patients are shown in Table 1  In AP group, the average fever duration were 6.22 ± 2.17 days, however patients in coinfection group had a fever with 7.10 ± 2.98 days, leading to a signi cantly longer duration of fever(p=0.03).there were 12 cases of the symptom of the shortness of breath in single AP group, and 19 cases in another group, indicating Shortness of breath was more commonly found in the coinfection group(P = 0.023).there was no statistical difference in pulmonary signs such as lung rales and wheezes between the two groups (P > 0.05),as shown in Table 2.

laboratory and pulmonary imaging examination
Although There were no statistical differences in the blood tests such as leukocyte counts, CRP, PCT, LDH, Hb, albumin, ALT, CK-MB between the two groups(P>0.05), pulmonary imaging, such as pulmonary consolidation, atelectasis, pleural effusion and multi lobe lesions were more common in the coinfection group (P < 0.05), as shown in Table 3. Normal range WBC 4-12*10^9/L; CRP 0-10mg/L; LDH 0-250mmol/L; PCT <0.25mg/L

medication
The patients with coinfection had a more severe symptom, leading to a signi cantly longer hospitalization time, and increasing the proportion of patients using glucocorticoids and / or gamma globulin, needing oxygen inhalation(P < 0.05). All children in two groups were cured and discharged without mechanical ventilation treatment, as shown in Table 4.

Discussion
Adenovirus(ADV) is a kind of double stranded DNA virus without outer shell, which is widely distributed in nature. It is mainly transmitted by air droplets. ADV is a important pathogen that causes communityacquired pneumonia in children.
Severe or refractory ADV infection cases can cause a series of multiple organ injury or even death [7,8].
Pneumonia caused by adenovirus is often accompanied by coinfected MP [3,9]. Whether infect Adenovirus is related to the host's age and immune function. coinfection makes the clinical manifestations of adenovirus pneumonia more complex.
Adenovirus pneumonia is common in children aged from 6 months to 5 years, especially those under 2 years old, which was found more cases in male patients [2,10]. In the present study, the age of patients in single AP group was signi cantly younger than those in coinfected MP group, considering that there was general lack of speci c antibody against adenovirus in young children, and MP commonly infected older children [11]. both of the two groups showed that there were more male patients than females, but there were no remarkable differences in gender distribution in the two groups. The distribution of adenovirus infection is global. Season is an important factor affecting adenovirus infection. The seasonal distribution of adenovirus infection varies in different regions and climate [12][13][14]. The data of our research shows that adenovirus infection occurs in all seasons throughout the year, the lowest infection rate is in autumn and the highest rate is in spring and summer, which are basically consistent with the literature reports. However, there was still a difference between the two groups. The incidence rate in the single AP group was the highest in spring, and the incidence rate of coinfection group was the highest in summer, which was consistent with the epidemic of mycoplasma pneumonia in southern China [15]. It was suggested that the etiology examination should be perfected in the high incidence season of the pathogen infection.
Fever is a manifestation of the body's resistance to in ammation, which is often used to judge the progress or outcome of the disease. It should be noted that compared with the single AP group, those who were coinfected with MP has a longer fever duration, though both groups of children have fever. thus, coinfection may lead to prolong the time of pathogen clearance and aggravate the host immune response, resulting in more internal and exogenous pyrogen. Our study found that the proportion of shortness of breath in coinfection group which led to higher oxygen inhalation therapy was signi cantly higher than that in single AP group, which is similar to the results of previous research [16]. It could be seen that MP coinfection aggravates the lung damage caused by adenovirus infection, which leads to the decline of alveolar ventilation function. Adenovirus infection may cause results as fellows: moist rales or wheezing are heard during physical examination, WBC can be normal, elevated or decreased, CRP and PCT can be increased or normal, liver and kidney function are abnormal, imaging examination can be seen large high-density shadow and pleural effusion changes [6]. The present study showed that both AP group and MP coinfection group had the similar result of pulmonary signs and laboratory tests such as WBC, CRP, LDH, ALB, CK-MB. Therefore, it is di cult to distinguish whether AP patients are coinfected with Mycoplasma pneumoniae from pulmonary signs and routine blood test. However, the coinfection group was more likely to cause lung consolidation, atelectasis, pleural effusion changes, and multiple lung lobe lesions, which suggested that Mycoplasma pneumoniae infection could further aggravate the pulmonary in ammatory exudation of children with adenovirus pneumonia through direct injury or indirect immune reaction.
At present, supporting symptomatic treatment is the main therapy for AP patients because of lacking of effective antiviral drugs [17,18]. Intravenous immunoglobulin can inhibit the production of cytokines, neutralize in ammatory factors, antigens and toxins, and participate in the regulation of immune response; glucocorticoid can inhibit excessive immune in ammatory response. Previous researches [18,19]con rmed that the use of glucocorticoid or immunoglobulin in the treatment of adenovirus pneumonia has a certain effect, which can reduce complications and improve the prognosis. In this study, the use of immunoglobulin and / or glucocorticoid in coinfection group is more than that in single AP group. Adenovirus has strong virulence and cause high mortality, which is an important pathogen leading to severe pneumonia in children. Studies have found that the incidence of dyspnea in adenovirus pneumonia is as high as 40.7%, even requiring ECMO treatment [20,21]. Our data indicates that the incidence of severe symptom of coinfection group is higher than single AP group, and hospitalization in coinfection group is also prolonged accordingly, suggesting that mixed MP infection is one of the risk factors of adenovirus pneumonia which is similar to the results of Previous researches [4]. There were no death and no mechanical ventilation after active treatment in both groups, it is suggested that the prognosis of most children with AP whether mixed with MP infection or not is well as the treatment is timely and appropriate.
Nevertheless, this study has several limitations. First, this study was performed at a single center in a single year, and the distribution of pathogens was greatly in uenced by the region and climate. In addition, the sample size was relatively small. Furthermore, our study belongs to retrospective study, lacking Rigorous design.
As mentioned above, AP coinfected with Mycoplasma pneumoniae may lead to prolonged fever duration because of aggravation of systemic in ammatory response, and MP infection play an important role in aggravation of disease in AP children. The key to improve prognosis is to identify whether Mycoplasma pneumoniae coinfection, and adopt positive and targeted treatment strategies.