Loosli IX 
Aerobiology and Secondary Infection 
by 
Clayton G-. Loosli, M, D, 
Assistant Professor of Medicine 
University of Chicago 
Intramural aerobiology has become increasingly important as 
a result of accumulating evidence which indicates that air 
may be the chief vehicle for the dissemination of pathogenic 
bacteria which contaminate wounds and burns, and which cause 
primary and secondary infections of the respiratory tract. 
In World War I delayed deaths among gas casualties were due 
principally to secondary infection of the lungs. Among the 
gassed victims, who did not succumb, infection is considered 
to have played an important role in producing the residual 
changes in the lungs such as bronchitis, emphysema, and 
fibrosis. Likewise the great majority of deaths following 
influenza and measles during the last war were due to secondary 
bacterial infections of the lungs. 
The pathological reaction elicited by the irritant gases, es- 
pecially mustard gas, in the pulmonary tract is similar in 
many respects to that described in the lungs of cases dying 
of measles and, especially, of influenza. These changes 
render the victims highly susceptible to infections with 
respiratory pathogens. The protective lining of the air 
passages and the eliminative mechanisms of the lungs are 
destroyed by the viral and chemical agents. The necrotized 
epithelial cells which once lined the trachea and bronchi and 
the edema fluid which oozes into the air passages from the 
underlying swollen connective tissue provides an excellent 
culture medium and fertile field for growth of organisms. In 
these cases pneumonia inevitably follows the aspiration or 
inhalation of infected eocudate containing pathogenic bacteria 
from the upper air passages into the already irritated and 
congested lung parenchyma. 
The bacterial flora found in the lungs of cases dying of 
pneumonia following influenza and gas poisoning is similar to 
that found in the nose and throat. Usually one of the patho- 
genic organisms associated with upper respiratory tract in- 
fections were recovered. ,In some camps hemolytic strepto- 
cocci predominated while in others influenza bacillus, 
pneumococci, and staphylocci were recovered in the majority 
of cases. Occasionally Fried?.anders bacillus was found. In 
the lungs of gassed victims dying of secondary pneumonia, on 
the other hand, hemolytic streptococci, and pneumococci were 
rarely recovered. Predominantly non-hemolytic streptococci 
and other organisms considered non-pathogenic and normal 
inhabitants of the nose and throat were present. The patho- 
genic organisms causing the secondary pulmonary infections 
in influenza and measles patients were generally considered 
to have been already present in the noses or throats before 
Mi-7855 Loosli IX 
they contracted their primary disease, or were acquired hy 
inhalation of infectious droplets from direct or close contact 
with infected individuals or carriers among the doctors, nurses, 
attendants and fellow patients. In many cases, however, the 
organisms were acquired after admission to clean hospital wards 
under strict isolation precautions. This was also true in cases 
of secondary infections of fracture wounds and presumably also 
occurred in some cases of delayed secondary pneumonia following 
gassing. 
The spread of respiratory disease by inhalation of infectious 
droplets was generally considered to occur only as a result of 
close contact. In the past decade, however, air contaminated 
with pathogenic bacteria and viruses has been shown to be the 
spread of certain diseases. Recent investigations have shown 
that in sneezing, coughing and talking both well and ill persons 
expel into the air large numbers of saliva droplets containing 
microorganisms. The smaller droplets dry and remain suspended 
in the air as droplet nuclei. The larger ones fall to the floor, 
evaporate and may become resuspended in the air as dust. These 
droplet nuclei and dust particles containing bacteria or virus ■ 
may be conveyed through the air for long distances. Dried 
saliva particles which float in the air from individuals with 
respiratory disease may contain pathogens and therefore con- 
stitute a potential source of infection. The bacterial content 
of the air in schools, hospital wards and institutions is 
roughly proportional to the degree of occupancy and activity. 
The number of pathogenic bacteria in the air are in general 
proportional to the number of respiratory infections among the 
occupants, but are small compared to the total air flora. Such 
pathogens may, however, remain viable in the dust for long ueriods 
of time. 
Although actual proof of aerial spread of infection is difficult 
to establish, clinical and bacterial studies made in an effort 
to control cross infection in hospitals indicate that droplet 
nuclei and infectious dust particles may be of special importance 
in the spread of viral agents and bacteria such as streptococci, 
diphtheria bacilli and staphylococci. Spread of measles and chicken 
pox have been shown to occur under conditions where direct and 
indirect contact was excluded. In general the spread of these 
diseases followed the flow of air currents. Hemolytic streptoco- 
ccal infection outbreaks in hospitals have been described where 
the disease spread from one floor to another in the direction of 
air currents. Relapses and complications in scarlet fever patients 
in wards have been shown to be due to reinfections with different 
types of streptococci. Such types were recovered from the ward 
dust and air. A case of streptococcus infection has been re- 
ported in a ward attendant who swept out a room five days follow- 
ing the discharge of a patient who had a hemolytic streptococcus Loosli IX 
infection of the same type. Likewise, cross infections in 
diphtheria wards were shown to he due to reinfection with 
another type of diphtheria bacillus. Similar types were 
recovered from the floor dust in large numbers at the time 
the cross infections occurred. 
Rapid increase in secondary streptococcal infections of burns 
after patients were admitted to the hospital were found to be 
due to cross infections from cases already present. Organisms 
recovered from the air and dust yore similar to those causing 
the complications. Likewise it has been shown that many 
hemolytic streptococcus infected war wounds occurred after 
admission to the hospital and wore cross infections from types 
of streptococci present in the air and dust of the wards. The 
rough handling of dry dressings from infected wounds and burns 
results in the liberations of many organisms into the air. 
The presence of large numbers of viable and virulent hemolytic 
streptococci have been demonstrated on blankets and dust in 
the wards containing streptococcus infected patients. The 
sweeping of the floor, changing bed clothes, and making beds 
in the infected patients rooms causes a marked increase in 
the bacterial content of the air. Such dust particles con- 
taining pathogens may remain and float on blanket lint for 
long periods. Many thousands of pathogenic organisms may be 
present in one gram of dust. In studies of simulated room 
environments viable and virulent hemolytic streptococci have 
been recovered several weeks after introduction into room air. 
Direct evidence of the aerial spread of disease can be obtained 
only under well controlled experimental conditions. Although 
the spread of influenza during the 1918 epidemic was considered 
to have been transmitted most likely by droplet infection, 
actual proof was lacking. Since the isolation of the influenza 
virus, however', clinical influenza has been produced in human 
volunteers following inhalation of air, containing virus. 
Aerial transmissions in ferrets and mice can be readily demon- 
strated by merely exposing these animals to atmospheres into 
which influenza virus has been sprayed as fine droplets. Under 
certain conditions the influenza virus may remain in room air 
retaining its potency to infect and kill mice placed in the 
rooms several hours after its introduction into the air. Mice 
normally are not susceptible to streptococci and pneumococci 
sprayed in the air in relatively large numbers. However, when 
given a sublethal influenza A infection they become highly 
susceptible to secondary bacterial infection and die of exten- 
sive pneumonia when allowed to breathe the bacteria-laden air. 
The above clinical, bacteriological and experimental evidence 
shows that if secondary infections of various types are to be 
prevented, the bacterial and viral content of the air in which 
M*-7855 Loosli IX 
susceptible to respiratory tract infection from the inhalation 
of air-borne pathogens as are others whose open wounds and 
burns become so readily infected from contaminated air. In 
preventing secondary infections, it is important to recognize 
that the infective agent may be conveyed through the air as 
droplets, droplet nuclei or dust particles. All means should 
be applied which will keep the bacterial content in the air 
below the infective level. The following are some of the 
more important recommendations of numerous investigators for 
the control of secondary infections* 
Measures which help to control droplet infection; 
1. Segregation and if possible Isolation of all patients. 
2. All attendants, doctors, nurses, orderlies• and 
visitors should be adequately masked (Canton flannel) 
and gowned, 
3. Attendants should be free from upper respiratory in- 
fections or gripue, sore throat or common cold, 
4. Adequate spacing of beds with barriers between beds. 
5. Isolation and prompt treatment with sulfonamide 
therapy of patients who contract a secondary in- 
fection with determination of etiological agent 
when possible. 
6. Masking of patients during wand cleaning and bed 
making. 
Measures designed to control the dispersal of dust borne par- 
ticles and droplet nuclei in the air; 
1. Oiling of floors. 
2. Sweeping with oiled or moistened brooms and bacterici- 
dal sweeping compounds. 
3. Treating blankets and bed clothes with oil preparations, 
bactericidal compounds. 
4. Careful handling rand disposal of infected dressings. 
5. Adequate ventilation with sufficient air changes to 
prevent the building up of high bacterial concen- 
tration in the air. 
Measures designed to sterilize the room air: 
1. Adequately lighted (daylight) wards and rooms. 
2. Ultraviolet radiation. 
3. Germicidal agents employed as mists or aerosals. 
a. Propylene glycol, one part in from 2 to 10 
million parts of air. 
b. Triethylene glycol in one to two hundred 
million parts of air. 
Under stress of emergency many of the above principles and 
M-7855 Loosli IX 
measures designed to prevent and control secondary infections 
following gassing may not "be practical. As many as possible, 
however, should be tried if good results are to be attained. 
Because of the high susceptibility of gassed patients to secon- 
dary infections of the pulmonary tract, careful clinical control 
should be exercised in their management. Daily observations 
should be made to detect early any pneumonias which may develop. 
Fever, cough, increased respiratory and pulse rate and leucocy- 
tosis indicate a pulmonary infection. If possible the patient 
should be placed under strict isolation and prompt treatment 
with sulfonamides instituted. If laboratory facilities are 
available the etiological agents causing-the pneumonia should 
be ascertained as an aid to prognosis and drug treatment. In 
secondary pneumonias follov/ing exposure to pulmonary irritants, 
the flora is often mixed and therefore a drug with the wide 
range of effectiveness which produces the fewest complications 
should be used. Sulfadiazine is no\/ generally recommended as 
the first choice in the treatment of pneumonia where the 
etiological agents are not determined, as well as in those 
cases caused by hemolytic streptococci, pneumococci, staphyloco- 
cci, influenza bacillus or Friedlanders bacillus. The dosage 
of drug recommended is the same as that used in the treatment of 
the primary pneumonias. Four grams is given as the initial dose 
followed by one gram every four hours until seventy-two hours 
after the temperature has returned to normal. Whether the recom- 
mended schedule of treatment should be continued would depend 
on the clinical course of the patient. Blood drug levels 
should be determined where possible to be sure of adequate 
therapy. Where sulfadiazine is not available sulfathiazole is 
the next drug of choice with the third choice being sulfapyridine. 
Regardless of the drug used the dosage is the same. 
Whether the sulfonamide drugs should be given prophylactically 
as a pneumonia preventative to gassed victims is problematical. 
It would seen .advisable in case of a hemolytic streptococcus 
throat or pneumonia outbreak in a. ward. However, if careful 
clinical observations are made the secondary pneumonias in these 
cases can be detected early enough to bring about favorable 
results with sulfonamide treatment after the diagnosis is made. 
If a sulfonamide drug is to be used prophylactically the dosage 
should be essentially the sane as used during treatment; four 
grams as an initial dose followed by one gram every six hours. 
When using sulfonamide drugs in the treatment of pulmonary in- 
fections the possible complications should be kept clearly in 
mind. Adequate fluid out-put (over 1000 cc. a day) is highly 
essential to avoid renal complications. The sulfonamides should 
not be considered as a substitute for other accepted procedures 
in the treatment of complications such as drainage of abscesses 
and emphysema cavities. 3-eneral medical measures should not be 
neglected in treatment of these pneumonias with sulfonamide drugs. 
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