What is pus

Pus is a collection of fluid, white blood cells, microorganisms, and cellular material that indicates the presence of an infected wound or abscess. Pus contains the germs, fluids, and cells the body has shed — basically anything that the body wants to get rid of.

Although pus is normally of a whitish-yellow hue, changes in the color can be observed under certain circumstances. Pus is sometimes green because of the presence of myeloperoxidase, an intensely green antibacterial protein produced by some types of white blood cells. Green, foul-smelling pus is found in certain infections of Pseudomonas aeruginosa. The greenish color is a result of the bacterial pigment pyocyanin that it produces. Amoebic abscesses of the liver produce brownish pus, which is described as looking like “anchovy paste”. Pus from anaerobic infections can more often have a foul odor ¹.

In almost all cases when there is a collection of pus in the body (abscess), the clinician will try to create an opening to drain it.

An abscess is a cavity filled with pus (pyoderma or sepsis). An abscess contains white blood cells, dead tissue and bacteria. Abscesses can form on the skin, under the skin, in a tooth, or inside the body. Some people feel sick when they have an abscess. They might get a fever that makes them feel too hot or too cold.

Cutaneous abscesses may occur anywhere on the skin, but are most common under the arms, at the base of the spine (pilonidal disease) or around the genitals (e.g. Bartholin abscess) and anus.

An abscess usually presents as a hot, red, swollen and painful lump. It may lead to fever, swollen lymph nodes, and illness including potentially dangerous septicemia. Non-bacterial abscesses may be cool, skin colored and painless.

If not treated, an abscess eventually bursts and drains thick yellow pus.

Although it may become ‘walled off’ by an inflammatory reaction, an abscess is not surrounded by a true capsule.

Is pus bad?

Yes. A collection of pus in your brain may progress to meningitis, cortical venous thrombosis, or brain abscess. Without treatment, coma and death occur rapidly, particularly in subdural empyema.

What causes pus

A painful abscess is usually due to acute bacterial infection. Bacteria penetrate a break in the skin such as a puncture wound, or via a hair follicle. Abscess may also develop around a foreign body, such as a splinter.

The most common causes of infective abscesses are:

• Staphylococcus aureus; the usual cause of boils (furuncles and carbuncles, the most common form of cutaneous abscess), wound infection or infected eczema.
• Methicillin resistant Staphylococcus aureus (MRSA), which may cause recurrent abscesses.
• Streptococcus pyogenes; the usual cause of cellulitis and erysipelas
• Mycobacterium tuberculosis (TB) and atypical mycobacterial infection
• Anaerobes, gram negative organisms, rare bacterial infections and mixed infections
• Fungal infection, eg kerion
• Severe viral infection eg herpes simplex
• Infestations or parasitic infections

In most mucus membranes, anaerobes outnumber aerobic and facultative bacteria in ratios ranging from 10:1 to 10,000:1, with anaerobic gram-negative bacilli microorganisms predominating ². Species of the Bacteroides fragilis group that colonize the gastrointestinal tract are usually isolated in intra-abdominal and rectal abscesses; pigmented Prevotella, Porphyromonas, and Fusobacterium spp. that colonize the oral cavity are present mainly in oral cavity abscesses, and Prevotella bivia and Prevotella disiens that predominate in the cervical canal are most often recovered in pelvic abscesses. The predominant aerobes and facultative organisms in abdominal and rectal abscesses are Enterobacteriaceae and staphylococci, and Neisseria gonorrhoeae are common in pelvic abscesses (Table 1). Fungi (e.g., Aspergillus) and protozoa (e.g., Toxoplasma gondii, particularly in HIV-infected patients) can also cause abscesses.

Table 1. Predominant bacteria from abscesses

	Abdominal								Urogenital				Head and neck
Parameter	Abdomen	Retroperitoneal	Diverticulitis	Perirectal	Liver	Spleen	Pancreatic	Subphrenic	Burtholm’s cyst	Prostate	Testicular	Scrotal	Periapical	Cervical lymphadenitis	Parotic	Peritonsillar	Retropharyngeal
Reference	6	20	19	25	23	23	21	24	6	6	6	6	26	22	28	29	10
No. of patients	83	161	22	144	48	29	46	52	26	3	6	15	32	40	23	34	14
No. of aerobic bacteria
S. pyogenes		1		9	3	1		4				1		4	1	10	3
Enterococcus spp.		19	3	9	8	3	11	9		1		5
S. aureus		11	1	34	4	4	6	5	2		1	5	1	8	8	6	5
M. catarrhalis																5	2
Haemophilus spp.	1												2		2	7	4
E. coli	57	60	15	19	11	5	18	28	6	2				1	1
K. pneumoniae	8	20	3	3	5	3	12	3	2					1
P. aeruginosa	4	9	1	4	2	1	5	3				2		1
Enterobacter spp.	1	8		1			4	4	1
Proteus spp.	2	8	1	12	2	3	3	4	3	1		1
S. marcescens		6	1		3		3	3
N. gonorrhoeae		4		2	1				4
Other		20	2	16		1	6	2	3	2
Enterobacteriaceae
Subtotal	107	204	35	131	43	23	77	83	24	6	3	15	23	18	16	49	26
Anaerobic bacteria
Peptostreptococcus spp.	24	95	6	72	18	11	26	33	12	1	3	7	18	5	5	16	18
Veillonella spp.	2	10	1	6	3	1	6	6	2			1	2	1		5	3
Eubacterium spp.	2	6	1	11			1	4				1	2		1	1	4
P. acnes		13		2	3	3	4	4					1	4	4	3	1
C. perfringens	6	10	2	4	5	2	4	6	1
Clostridium spp.	13	13	3	11	5	1	3	7				2					2
Fusobacterium spp.	4	14	1	21	10	3	5	5	2				9		3	11	14
B. fragilis	47	34	14	58	7	2	6	11	3	1	1	1	1	1	1	1
B. fragilis groupa	11	32	7	27	6	3	11	14	2	1	2		1
P. melaninogenica	5	5	2	18	1	1	2	2	2		1	2	3	3	1	7	10
P. intermedia		7		12	2	2	3	3	1			1	2	2	3	3	4
P. asaccharolytica	4	3	1	20					3		1	2	1	2		5	4
P. oralis		2		2					1			1	4			1	3
P. disiens		1		6	1		1	1
P. bivia		2		14					4		3
Bacteroides spp.	3	12	1	19			4	7	6	1		6	4	2	1	4	11
P. gingivalis													7
Subtotal	128	268	37	325	73	33	81	111	43	4	8	28	55	24	20	58	78
Total	235	472	72	256	116	56	158	194	67	10	11	33	78	42	36	107	104

Footnote: a) Other than B. fragilis.

[Source ² ]

Infective abscesses may affect healthy people, but they are more common in the following circumstances.

• Metabolic syndrome and obesity
• Smoking
• Diabetes
• Immune compromise
• IV drug users

A sterile abscess may persist after infection has been cleared, as it contains dead or necrotic tissue and inflammatory cells.

Sterile abscess may occur after corticosteroid injection. This is more likely when the medication has spilled into subcutaneous fat. A foreign-body or other hypersensitivity reaction to injected material such as bovine collagen may also result in abscess formation.

Certain inflammatory skin diseases may cause tissue destruction and abscess formation, in the absence of pathogens (infectious microbes). These include:

• Hidradenitis suppurativa
• Acne conglobata and acne fulminans
• Crohn skin disease
• Panniculitis (inflamed subcutaneous fat)

How to get rid of pus

An abscess should be explored to remove foreign bodies, and its contents should be removed. This requires making a surgical incision and draining the pus. The cavity is then thoroughly washed out with saline. It should be left open to allow further pus to drain away. Wicks are sometimes inserted if the abscess is deep, to help it drain.

Antibiotics are often prescribed, chosen according to the organism causing the abscess and its sensitivities.

Prevention of further abscess formation

If abscesses are due to staphylococcal infection, the risk of recurrence can be minimized by:

• Hygiene: wash hands frequently (or use hand rubs) and do not share towels, clothing, razors and tooth brushes.
• Reduce transmission to others: while infected, do not share equipment at a community gym or attend sauna or swimming pool.
• Dispose of tissues and dressings in sealed bag or burn them.
• Take care not to nick skin while shaving
• Eat plenty of fresh fruit and vegetables
• Aim for normal weight and do not smoke.

References

1. Topazian RG, Goldberg MH, Hupp JR (2002). Oral and maxillofacial infections (4 ed.). Philadelphia: W.B. Saunders. ISBN 978-0721692715.
2. Brook I. Abscesses. In: Brogden KA, Guthmiller JM, editors. Polymicrobial Diseases. Washington (DC): ASM Press; 2002. Chapter 9. Available from: https://www.ncbi.nlm.nih.gov/books/NBK2497