Codeigniter Checkbox

Can you guys tell me what i'm doing wrong here in my code? I tried to post the data inside these checkboxes to database

here is the view.php

(more code)
<div class="form-group">
          <label class="control-label col-md-3">Infection</label>
          <div class="col-md-9">
            <input type="checkbox" name="infectionType[]" value="vap"> VAP
            <input type="checkbox" name="infectionType[]" value="hap"> HAP
            <input type="checkbox" name="infectionType[]" value="isk"> ISK
            <input type="checkbox" name="infectionType[]" value="iad"> IAD
          </div>
        </div>

and this is my controller.php

public function insert_surveilance(){
    $data=array(
        (more code)
        'vap' => $this->input->post('vap'),
        'hap' => $this->input->post('hap'),
        'isk' => $this->input->post('isk'),
        'iad' => $this->input->post('iad'),
        (more code)
    );
    $data[]=
        $insert = $this->surveilance_model->insert_surveilance($data);
        echo json_encode(array("status"=>TRUE));
}

then this is my model.php

public function insert_surveilance($data){
    $this->db->insert($this->table, $data);
    return $this->db->insert_id();
}

this is the save function ... function save(){

    var url;
    if(save_method == 'add'){
      url="<?php echo site_url('surveilance/insert_surveilance')?>";
    } else {
      url="<?php echo site_url('surveilance/edit_surveilance')?>";
    }
    $.ajax({
        url : url,
        type: "POST",
        data: $('#form').serialize(),
        dataType: "JSON",
        success: function(data)
        {
           //if success close modal and reload ajax table
           $('#modal_form').modal('hide');
          location.reload();// for reload a page
        },
        error: function (jqXHR, textStatus, errorThrown)
        {
            alert('Failed adding data');
        }
    });
  }